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HAND-BOOK 



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PHYSIOLOGY 






HAND-BOOK 



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PHYSIOLOGY 

BY WILLIAM SENHOUSE KIRKES, M.D. 



EDITED BY 

W. MORRANT BAKER, F.R.C.S. 

LECTURBR ON PHTSIOLOGY, AND 

ASSISTANT BTTROEOX TO ST. BARTHOLOMEW'S HOSPITAL SURGEON TO THE 

EVELINA HOSPITAL TOR SICK CHILDREN. 



WITH TWO HUNDRED AND FORTY-EIGHT ILLUSTRATIONS. 



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LONDON : 

JOHN MURRAY, ALBEMARLE STREET. 

1872. 



LOKDOX : 
BRAUBURY, AGKEAV, & CO., PRINTERS, WHITEIRIARS. 



PREFACE TO THE EIGHTH EDITION. 

♦ 

The Eighth Edition is the result of an increased 
demand for this work, involving the necessity for 
a reprint at an earlier period after the publication of 
the Seventh Edition than was anticipated. The oppor- 
tunity has been seized for making corrections and addi 
tions Avhere they appeared to be most needed ; but the 
present issue must be regarded as, in great part, a 
reprint of the Edition of 1869. 

W. MORRANT BAKER. 

The College, St. Bartholomew's Hospital, 
October, 1872. 



Digitized by the Internet Archive 

in 2007 with funding from 

IVIicrosoft Corporation 



http://www.archive.org/details/8thhandbookofphy00kirkuoft 



CONTENTS. 

♦ 

CHAPTER I. 

PAGE 

The General and Distinctive Characters of Living 

Beings i 

CHAPTER II. 
Chemical Composition of the Human Body ... 7 

CHAPTER III. 
Structur-Vl Composition of the Human Body . . 19 

CHAPTER IV. 

Structure of the Elementary Tissues 29 

Epithelium ib. 

Areolar, Cellular, or Connective Tissue .... 35 

Adi^Dose Tissue 38 

Pigment 39 

Cartilage 41 

Bones and Teeth 45 

CHAPTER V. 

The Blood 56 

Quantity of Blood 58 

Coagulation of the Blood 60 



Vlll CONTEXTS. 



The Blood, continued. 

Conditions affecting Coagulation 66 

Chemical Composition of the Blood .... 68 

The Blood-Corpuscles, or Blood-Cells 69 

Chemical Comi)Osition of Red Blood-Cells ... 74 

Blood-Crystals ib. 

Tlie "WTiite Corpuscles 76 

The Serum 78 

Variations in the Principal Constituents of the Liquor 

Sanguinis 79 

Variations in Healthy Blood under DiflFerent Circumstances 83 
Variations in the Composition of the Blood in Different 

parts of the Body 84 

Gases contained in the Blood 89 

Development of the Blood 90 

Uses of the Blood 95 

Uses of the various Constituents of the Blood . . . ib,. 



CHAPTER VI. 

Circulation of the Blood . . .... 99 

The Systemic, Pulmonarj', and Portal Circulation . . iol 



The Heart 102 

Structure of the Valves of the Heart .... 104 

The Action of the Heart . . . . . . . 109 

Function of the Valves of the Heart . . . . 112 

Sounds of the Heart 1 19 

Impulse of the Heart 122 

Frequency and Force of the Heart's Action . . . 124 

Cause of the Rhythmic Action of the Heart . . . 128 

Effects of the Heart's Action 132 

The Arteries 133 

Structure of the Arteries ib. 

The Pulse 143 

Sphygmograph 146 

Force of the Blood in the Arteries 152 

Velocity of the Blood in the Arteries 155 



CONTEXTS. 



IX 



PAGE 

The Capillaries 155 

The Structure and Arrangement of Capillaries . . . 156 

Circulation in the Capillaries ...... i6o- 

The Veins 167 

Structure ib. 

Agents concerned in the Circulation of the Blood . . 1 73^ 

Velocity of Blood in the Veins 175 

Velocity of the Circulation 176 



Peculiarities of the Circulation in Different Parts 180 

Cerebral Circulation ib. 

Erectile Structures 183 



CHAPTER VII. 



KeSI'I RATION 

Position and Structure of the Lungs . 
Mechanism of Respiration .... 
Respiratory Movements .... 

Respiratory Rhythm 

Respiratory Movements of Glottis 
Quantity of Air respired .... 

Movements of the Blood in Respiratory Organs 
Changes of the Air in Respiration . 
Changes produced in the Blood by Kespii'ation 
Mechanism of various Respiratory Actions 
Influence of the Nervous System in Respiration 
Effects of the Suspension and Arrest of Respiration 



186 

ib. 
194 

195 
200 
ib. 
201 
208 
210 
219 
220 
225 
227 



CHAPTER VIII. 



Animal Heat 231 

Variations in Temperature ...... 232 

Sources and Mode of Production of Heat in the Body . . 236 

Regulation of Temperature . . . . . . 238 

Influence of Nervous System 243 



CONTENTS. 



CHAPTER IX. 

PAGE 

Digestion 245 

Food ' i^' 

Starvation 250 

Passage of Food through the Alimentary Canal . . 256 

The Salivary Glands and the Saliva .... ih. 

Passage of Food into the Stomach 263 

Digestion of Food in the Stomach 265 

Structure of the Stomach ib. 

Secretion and Properties of the Gastric Fluid . . . 271 

Changes of the Food in the Stomach 280 

Movements of the Stomach 287 

Influence of the Nervous System on Gastric Digestion . 291 

Digestion of the Stomach after Death .... 294 

Digestion in the Intestines 297 

Structure and Secretion of the Small Intestines . . ih. 

Valvulaj Conniventes 298 

Glands of the Small Intestine 299 

The Villi 306 

Structui-e of the Large Intestine 309 

The Pancreas and its Secretion 312 

Structure of the Liver 314 

Functions of the Liver 322 

The Bile ih. 

Glycogenic Function of the Liver 333 

Summary of the Changes which take place in the Food 

during its Passage through the small Intestine . . 337 

Summary of the Process of Digestion in the large Intestine 340 

Gases contained in the Stomach and Intestines . . . 343 

Movements of the Intestines 344 



CHAPTER X. 

Absorption 347 

Structiu-e and OflUce of the Lacteal and Lymphatic Vessels 

and Glands ih. 

Lymphatic Glands 354 



CONTENTS. XI 



Absorption, continued. 

Properties of Lympli and Chyle 357 

Absorption by the Lacteal Vessels 363 

Absorption by the Lymphatics 364 

Absorption by Blood- Vessels 367 



CHAPTER XL 

KUTRITION AND GrOWTII 374 

Nutrition ib. 

Growth 390 



CHAPTER XIL 

vSecretion 394 

Secreting Membranes 395 

Serous Membranes 396 

Mucous Membranes 398 

Secreting Glands 401 

Process of Secretion 404 



CHAPTER XIIL 

Vascular Glands ; or Glands without Ducts . . . 410 

Stracture of the Spleen 411 

Puuctions of the Vascular Glands . . ... 414 



CHAPTER XIV. 

The Skin and its Secretions 419 

Structure of the Skin . . . . . . . ib. 

Structure of Hair and Nails 428 

Excretion by the Skin 432 

Absorption by the Skin 437 



xii CONTEXTS. 



CHAPTER XY. 

The Kidneys and their Secretion 
Structure of the Kidneys 
Secretion of UriHe .... 
The Urine ; its general Properties . 
Chemical Composition of the Urine . 



PAaR 
440 

ib. 

446 

448 

45^ 



CHAPTER XVI. 

The Nervous System 463 

Elementary Stmctures of the Nervous System . . . 464 

Functions of Nerve-Fibres 474 

Functions of Nerve-Centres 483 

Cerebro-Si'Inal Nervous System. . . . . . 488 

Spinal Cord and its Nerves iK 

Functions of the Spinal Cord 495 

The Medulla Oblongata , . 50^ 

Its Stnicture . . . . . . ... ib. 

Distribution of the Fibres of the Medulla Oblongata . 511 

Functions of the Medulla Oblongata 513 

Structure and Physiology of the Pons Varolii, Crura 
Cerebri, Corpora Quadrigemina, Corpora Genicu- 

lata, Optic Thalami, and Corpora Striata . . . 518 

Pons Varolii »6. 

Cmra Cerebri ib. 

Corpora Quadrigemina 520 

The Sensory Ganglia 523 

Structure and Physiology of the Cerebellum . . 524 

Structure and Physiology of the Cerebrum . . 531 

Physiology of the Cerebral and Spinal Nerves . . 538" 
Physiology of the Third, Fourth, and Sixth Cerebral or 

Cranial Nerves 539 

Physiology of the Fifth or Trigeminal Nerve . . . 543 

Physiology of the Facial Nerve 550 



CONTENTS. xiii 



Physiology of the Ceeebral and Spinal Nerves, contviued. 

Physiology of the Glosso-Pharyiigeal Nerve . . . 553 

Physiology of the Pneumogastric Nerve . . . . 557 

Physiology of the Spinal Accessory Nerve . . . 564 

Physiology of the Hypoglossal Nerve 565 

Physiology of the Spinal Nerves 567 

Physiology of the Sympathetic Nerve .... ih. 



CHAPTER XVII. 

Causes and Phenomena of Motion 578 

Ciliary Motion ih. 

Muscular Motion 580 

Muscular Tissue ib. 

Properties of Muscular Tissue . . . . . 587 

Action of the Voluntary Muscles . .... 595 

Action.of the Involuntary Muscles .... 602 

Source of Muscular Action ih. 



CHAPTER XVIII. 

Of Voice and Speech 6o4 

Mode of Production of the Human Voice .... ib. 

The Larynx 606 

Application of the Voice in Singing and Speaking . . 614 

Speech 619 



CHAPTER XIX. 

The Senses 622 

The Sense of Smell 630 

The Sense of Sight . 636 

Structure of the Eye ih. 

Phenomena of Vision . 645 

Reciprocal Action of different parts of the Retina . 661 

Simultaneous Action of the two Eyes . . . . 664 



xiv CONTENTS. 

PAGE 

The Sense of Hearing 617 

Anatomy of tlie Organ of Hearing ib. 

Physiologj^ of Hearing 679 

Functions of the External Ear 681 

Functions of the Middle Ear ; the Tympanum, Ossicula, 

and Fenestra 683 

Functions of the Internal Ear 689 

Sensibility of the Auditory Nerve 692 

The Sense of Taste 697 

The Sense of Touch 706 



CHAPTER XX. 

Generation and Development 713 

Generative Organs of the Female 714. 

Unimpregnated Ovum 718 

Discharge of the Ovum 723 

Corpus Luteum 727 

Impregnation of the Ovum 731 

Male Sexual Functions ih. 

Development 739 

Changes of the Ovum previous to the Formation of the 

Embryo ih. 

Changes of the Ovum within the Uterus .... 742 

The Umbilical Vesicle 745 

The Amnion and Allantois 747 

The Chorion 751 

Changes of the Mucous Membrane of the Uterus and 

Formation of the Placenta 7^2 

Development of Organs 758 

Development of the Vertebral Column and Cranium . ih. 

Development of the Face and Visceral Arches . . . 760 

Development of the Extremities ..... 762 



CONTENTS. 



XV 



Development of Oegans, continued. 
Development of the Vascular System 
Circulation of Blood in the Foetus .... 
Development of the Nervous System 
Development of the Organs of Sense 
Development of the Alimentary Canal 
Development of the Kespiratory Apparatus 
The Wolffian Bodies, Urinary Apparatus, and Sexual Organs 



763 
767 

770 
ib. 

773 
776 

777 



The Mammary Glands 



782 



Index .... 

List of Woeks eefeeked to 



787 
825 



HANDBOOK OF PHYSIOLOGY, 



CHAPTER I. 

ON THE GENEEAL AND DISTINCTIVE CIIAEACTEKS OF 
LIVING BEINGS. 

Human Physiology is tlie science wMcli treats of the 
life of man — of the way in which he lives, and moves, and 
has his being. It teaches how man is begotten and born ; 
how he attains maturity ; and how he dies. 

Having, then, man as the object of its study, it is un- 
necessary to speak here of the laws of life in general, and 
the means by which they are carried out, further than is 
requisite for the more clear understanding of those of the 
life of man in particular. Yet it would be impossible to 
understand rightly the working of a complex machine 
without some knowledge of its motive power in the sim- 
plest form ; and it may be well to see first what are the 
so-called essentials of life — those, namely, which are mani- 
fested by all living beings alike, by the lowest vegetable 
and the highest animal, before proceeding to the consider- 
ation of the structure and endowments of the organs and 
tissues belonging to man. 

The essentials of life are these, — birth, growth and 
development, decline and death — and an idea of what life 
is, will be best gained by sketching these events, each in 
succession, and their relations one to another. 

The term, birth, when employed in this general sense 
of one of the conditions essential to life, without reference 



/^ 



2 GROWTH. 

to any particular kind of living being, may be taken to 
mean, separation from a parent, with, a greater or less 
power of independent existence as a living being. 

Taken thus, the term, although not defining any par- 
ticular stage in development, serves well enough for the 
expression of the fact, to which no exception has yet been 
proved to exist, that the capacity for life in all living beings 
is got by inheritance. 

Growth, or inherent power of increasing in size, although 
essential to our idea of life, is not a property of living 
beings only. A crystal of sugar or of common salt, or of 
any other substance, if placed under appropriate conditions 
for obtaining fresh material, will grow in a fashion as 
definitely characteristic and as easily to be foretold as that 
of a living creature. It is, therefore, necessary to explain 
the distinctions which exist in this respect between living 
and lifeless structures; for the manner of growth in the 
two cases is widely different. 

First, the growth of a crystal, to use the same example 
as before, takes place merely by additions to its outside; 
the new matter is laid on particle by particle, and layer by 
layer, and, when once laid on, it remains unchanged. The 
growth is here said to be superficial. In a living structure, 
on the other hand, as, for example, a brain or a muscle, 
wiiere growth occurs, it is by addition of new matter, not 
to the surface only, but throughout every part of the mass; 
the growth is not superficial, but interstitial. In the second 
place, aU living structures are subject to constant decay ; 
and life consists, not as once supposed, in the power of pre- 
venting this never-ceasing decay, but rather in making up 
for the loss attendant on it by never-ceasing repair. Thus, 
a man's body is not composed of exactly the same particles 
day after day, although to all intents he remains the same 
individual. Almost every part is changed by degrees ; but 
the change is so gradual, and the renewal of that which is 
lost so exact, that no difference may be noticed, except at 



DEVELOPMENT. 3 

long intervals of time. A lifeless structure, as a crystal, 
is subject to no such, laws ; neither decay nor repair is a 
necessary condition of its existence. That which, is true of 
structures which, never had to do with life is true also with 
respect to those which, though, they are formed by living 
parts, are not themselves alive. Thus, an oyster shell is 
formed by the living animal which it encloses, but it is as 
lifeless as any other mass of saKne matter ; and in accord- 
ance with this circumstance its growth takes place not in- 
terstitially , but layer by layer, and it is not subject to the 
constant decay and reconstruction which belong to the 
living. The hair and nails are examples of the same 
fact. 

Thirdly. In connection with the growth, of lifeless 
masses there is no alteration in composition or properties 
of the material which is taken up and added to the pre- 
viously existing mass. For example, when a crystal of 
common salt grows on being placed in a fluid which con- 
tains the same material, the properties of the salt are not 
changed by being taken out of the liquid by the crystal 
and added to its surface in a solid form. But the case is 
essentially different from this in living beings, both animal 
and vegetable. A plant, like a crystal, can only grow when 
fresh material is presented to it ; and this is absorbed by 
its leaves and roots ; and animals for the same purpose of 
getting new matter for growth and nutrition, take food into 
their stomachs. But in both these cases the materials are 
much altered before they are finally assimilated by the 
structures they are destined to nourish. 

Fourthly. The growth of all living things has a definite 
limit, and the law which governs this limitation of increase 
in size is so invariable that we should be as much astonished 
to find an individual plant or animal without limit as to 
growth as without limit to life. 

Development is as constant an accompaniment of life as 
growth. The term is used to indicate that change to 

B 2 



4 AXIMxVLS COXTRASTED 

which, before maturity, all living parts are constantly sub- 
ject, and by which they are made more and more capable 
of performing their several functions. For example, a 
full-grown man is not simply a magnified child; his tissues 
and organs have not only grown, or increased in size, they 
have also developed, or become better in quality. 

No very accurate limit can be drawn between the end of 
development and the beginning of decline ; and the two 
processes may be often seen together in the same individual. 
But after a time all parts alike share in the tendency to 
degeneration, and this is at length succeeded by death. 

The decline of living beings is as definite in its occur- 
rence as growth or development. Death — not by disease 
or injury — so far from being a violent interruption of the 
course of life, is but the fulfilment of a purpose in view 
&om the commencement. 

It has been already said that the essential features of 
life are the same in all living things ; in other words, in the 
members of both the animal and vegetable kingdoms. It 
may be well now to notice briefly the distinctions which 
exist between the members of these two kingdoms. It 
aaay seem, indeed, a strange notion that it is possible to 
confound vegetables with animals, but it is true with 
respect to the lowest of them, in which but little is mani- 
fested beyond the essentials of life, which are the same in 
both. 

I. Perhaps the most essential distinction is the presence 
or absence of power to live upon inorganic material ; in 
other words, to act chemically on carbonic acid, ammonia 
and water, so as to make use of their component elements 
as food. Indeed one ought probably to say that a question 
concerning the capability of the lower kinds of animal to 
live in this way cannot be entertained; and that such 
a manner of life should decide at once in favour of a 
vegetable nature, whatever might be the attributes which 
seemed to point to an opi)osite conclusion. The power of 



WITH VEGETABLES. 5 

living upon organic matter would seem to be less decisive 
of an animal nature, for some fungi appear to derive 
support almost entirely from this source. 

II. There is, commonly, a marked difference in general 
chemical composition between vegetables and animals, 
even in their lowest forms ; for while the former consist 
mainly of a substance containing carbon, hydrogen, and 
oxygen only, arranged so as to form a compound closely 
allied to starch, and called cellulose, the latter are com- 
monly composed in great part of the three elements 
just named, together with a fourth, nitrogen ; the proxi- 
mate principles formed from these being identical, or 
nearly so, with albumen. It must not be supposed, how- 
ever, that either of these tj^ical compounds alone, with 
its allies, is confined to one kingdom of nature. Nitro- 
genous or albuminous compounds are freely produced 
by vegetable structures, although they form an infinitely 
smaller proportion of the whole organism than cellulose or 
starch. And while the presence of the latter in animals 
is much more rare than is that of the former in vegetables, 
there are many a,nimals in which traces of it may be dis- 
covered, and some, the Ascidians, in which it is found in 
considerable quantity. 

III. Inherent power of movement is a quality which we 
so commonly consider an essential indication of animal 
nature, that it is difficult at first to conceive it existing in 
any other. The capability of simple motion is now knowTi, 
however, to exist in so many vegetable forms, that it can 
no longer be held as an essential distinction between them 
and animals, and ceases to be a mark by which the one 
can be distinguished from the other. Thus the zoospores 
of many of the Cryptogamia exhibit movements of a like 
kind to those seen in animalcules ; and even among the 
higher orders of plants, many exhibit such motion, either 
at regular times, or on the application of external irrita- 
tion, as might lead one, were this fact taken by itself, to 



6 AIs^I]\[ALS COXTRASTED 

regard them as sentient beings. Inherent power of move- 
ment, then, although especially characteristic of animal 
nature, is, "when taken by itself, no proof of it. Of 
course, if the movement were such as to indicate any kind 
of purpose, whether of getting food or any other, the case 
would be different, and we should justly call a being ex- 
hibiting such motion, an animal. But low down in the 
scale of life, where alone there exists any difficulty in 
distinguishing the two classes, movements, although almost 
always more lively, are scarcely or not at all more pur- 
posive in one than the other ; and even if we decide on the 
animal nature of a being, it by no means follows that we 
are bound to acknowledge the presence of sensation or 
volition in the slightest degree. There may be at least 
no evidence of its possessing a trace of those tissues, 
nervous and muscular, by which, in the higher members 
of the animal kingdom, these qualities are manifested. 
Probably there is no more of either of them in the lowest 
animals than in vegetables. In both, movement is effected 
by the same means — ciliary action, and hence the greater 
value, for purposes of classification, of the power to live 
on this or that kind of food, — on organic or inorganic 
matter. As the main purpose of the lowest members of 
the vegetable kingdom is doubtless to bring to organic 
shape the elements of the inorganic world around, so the 
function of the lowest animal is, in like manner, to act on 
degenerating organic matter, — ''to arrest the fugitive 
organized particles, and turn them back into the ascending- 
stream of animal life." And, because sensation and voli- 
tion are accompaniments of life in somewhat higher animal 
forms, it is needless to suppose that these qualities exist 
under circumstances in which, as we may believe, they 
could be of no service. It is as needless as to dogmatise 
on the opposite side, and say that no feeling or voluntary 
movement is possible without the presence of those tissues 
which we call nervous and muscular. 



^^ITH VEGETABLES. 7 

IV. The presence of a stomacli is a very general mark 
by wliich an animal can be distinguished from a vegetable. 
But the lowest animals are surrounded by material that 
they can take as food, as a plant is surrounded by an 
atmosphere that it can use in like manner. And every part 
of their body being adapted to absorb and digest, they 
hb,ve no need of a special receptacle for nutrient matter, 
and accordingly have no stomacli. This distinction, then, 
is not a cardinal one. 

It would be tedious as well as unnecessary to enumerate 
the chief distinctions between the more highly developed 
animals and vegetables. They are sufficiently apparent. 
It is necessary to compare, side by side, the lowest mem- 
bers of the two kingdoms, in order to understand rightly 
how faint are the boundaries between them. 



CHAPTER II. 



CHEMICAL COMPOSITION OF THE HUMAN BODY. 

The following Elementanj Substances may be obtained by 
chemical analysis from the human body : Oxygen, Hydro- 
gen, Nitrogen, Carbon, Sulphur, Phosphorus, SiHcon, 
Chlorine, Fluorine, Potassium, Sodium, Calcium, Magne- 
sium, Iron, and, probably as accidental constituents, Man- 
ganesium, Aluminium, Copper, and Lead. Thus, of the 
sixty-three or more elements of which all known matter is 
composed, more than one-fourth are present in the human 
body. 

Only one or two elements, and in very minute amount, 
are present in the body uncombined with others; and 
even these are present much more abundantlj^ in various 
states of combination. The most simple compounds formed 



8 CHEMICAL COMPOSITION OF HUMAN BODY. 

by union in various proportions of these elements are 
termed jiroximate principles ; while the latter are classified 
as the organic and the inorganic proximate principles. 

The term organic was once applied exclusively to those 
substances which were thought to be beyond the compass 
of synthetical chemistry and to be formed only by or- 
ganized or living beings, animal or vegetable; these 
being caUed organized, inasmuch as they are charac- 
terized by the possession of different parts caHed organs. 
But with advancing knowledge, both distinctions have dis- 
appeared ; and while the title of living organism is apj^lied 
to numbers of Hving things, having no trace of organs in 
the old sense of the term, and in some, so far as can be 
now seen, in no other sense, the term organic has long 
ceased to be applied to substances formed only by living 
tissues. In other words, substances, once thought to be 
formed only by living tissues, are stiU termed organic, 
although they can be now made in the laboratory. The 
term, indeed, in its old meaning, becomes year by year 
applicable to fewer substances, as the chemist adds to his 
conquests over inorganic elements and compounds, and 
moulds them to more complex forms. 

Although a large number of so-caUed organic com- 
pounds have long ceased to be pecuHar in being formed 
only by living tissues, the terms organic and inorganic are 
stiU commonly used to denote distinct classes of chemical 
substances, and the classification of the matters of which 
the human body is composed into the organic and tlie 
inorganic is -convenient, and wiU be here employed. 

No very accurate line of separation can be drawn 
between organic and inorganic substances, but there are 
certain peculiarities belonging to the former which may 
be here briefly noted. 

I . Organic compounds are composed of a larger number 
of Elements than are present in the more common kinds of 
inorganic matter. Thus, albumen, fibrin, and gelatin, the 



CHEMICAL COMPOSITION OF HUMAN BODY. 9 

most abundant substances of this class, in the more liigbly 
organized tissues of animals, are composed of five elements, 
— carbon, hydrogen, oxygen, nitrogen, and sulphur. The 
most abundant inorganic substance, water, has but two 
elements, hydrogen and oxygen. 

2. Not only are a large number of elements usually 
combined in an organic compound, but a large number of 
equivalents or atoms of each of the elements are united to 
form an equivalent or atom of the compound. In the case 
of carbonate of ammonium, as an example among inorganic 
substances, one equivalent of carbonic acid is united with 
two of ammonium; the equivalent or atom of carbonic acid 
consists of one of carbon with two of oxygen ; and that of 
ammonium of one of nitrogen with three of hydrogen. But 
in an equivalent or atom of fibrin, or of albumen, there 
are of the same elements, respectively, y2, 22, 18, and 
112 equivalents. And together with this union of large 
numbers of equivalents in the organic compaund, it is 
further observable, that the several numbers stand in no 
simple arithmetical relation one with another, as the 
numbers of equivalents combining in an inorganic com- 
pound do. 

With these peculiarities in the chemical composition of 
organic bodies we may connect two other consequent facts; 
first, the large number of difierent compounds that are 
formed out of comparatively few elements ; secondly, their 
great proneness to decomposition. For it is a general 
rule, that the greater the number of equivalents or atoms 
of an element that enter into the formation of an atom of 
a compound, the less is the stability of that compound. 
Thus, for example, among the various oxides of lead and 
other metals, the least stable in composition are those in 
which each equivalent has the largest number of equiva- 
lents of oxygen. So, water, composed of one equivalent 
of oxj^gen and two of hydrogen, is not changed by any 
slight force; but peroxide of hydrogen, which has two 



lO CHEMICAL COMPOSITIOX OF HUMAN BODY. 

equivalents of oxygen to t\70 of hydrogen, is among the 
substances most easily decomposed. 

The instability, on this ground, belonging to organic 
compounds, is, in those which are most abundant in the 
highly organized tissues of animals, augmented, 1st, by 
their containing nitrogen, which, among all the elements, 
may be called the least decided in its affinities, and that 
which maintains with least tenacity its combinations with 
other elements ; and, 2ndly, by the quantity of water 
which, in their natural state, is combined with them, and 
the presence of which furnishes a most favourable con- 
dition for the decomposition of nitrogenous compounds. 
Such, indeed, is the instability of animal compounds, 
arising from these several peculiarities in their constitu- 
tion, that, in dead and moist animal matter, no more is 
requisite for the occurrence of decomposition than the 
presence of atmospheric air and a moderate temperature ; 
conditions so commonly present, that the decomposition of 
dead animal bodies appears to be, and is generally called, 
spontaneous. The modes of such decomposition vary ac- 
cording to the nature of the original compound, the tem- 
perature, the excess of oxygen, the presence of microscopic 
organisms, and other circumstances, and constitute the 
several processes of decay and putrefaction ; in the results 
of which processes the only general rule seems to be, that 
the several elements of the original compound finally unite 
to form those substances, whose composition is, under the 
circumstances, most stable. 

The organic compounds existing in the human body may 
be arranged in two classes, namely, the azotized or nitro- 
(jenous, and the non- azotized, or non-nitrogenous principles. 

The non- azotized principles include the several fatty, oily, 
or oleaginous substances, as olein, stearin, cholesterin, and 
others. In the same category of non-nitrogenous substances 
may be included lactic and formic acids, animal glucose, 
sugar of milk, &c. 



GELATINOUS SUBSTANCES. n 

The oily or fatty matter which, enclosed in minute cells, 
forms the essential part of the adipose or fatty tissue of the 
human body (p. 38), and which is mingled in minute par- 
ticles in many other tissues and fluids, consists of a mixture 
oi stearin, jpalmitin, and olein. The mixture forms a clear 
yellow oil, of which different specimens congeal at from 
45° to 35". 

Cholesterin, a fatty matter which melts at 293° F., and is 
therefore, always solid at the natural temperature of the 
body, may be obtained in small quantity from blood, bile, 
and nervous matter. It occurs abundantly in many biliary 
calculi ; the pure white crystalline specimens of these con- 
cretions being formed of it almost exclusively. Minute 
rhomboidal scale-like crystals of it are also often found 
in morbid secretions, as in cysts, the puriform matter of 
softening and ulcerating tumours, &c. It is soluble in 
ether and boiling alcohol; but alkalies do not change 
it ; it is one of those -fatty substances which are not 
saponifiable. 

The azotized or nitrogenous principles in the human body 
include what may be called the proper gelatinous and alhu- 
minous substances, besides others of less definite rank and 
composition, as pepsin and ptyalin, horny matter or keratin, 
many colouring and extractive matters, &c. 

The gelatinous substances are contained in several of the 
tissues, especially those which serve a passive mechanical 
office in the economy ; as the cellular, or fibro-cellular 
tissue in all parts of the body, the tendons, ligaments, 
and other fibrous tissues, the cartilages and bones, the 
skin and serous membranes. These, when boiled in 
water, yield a material, the solution of which remains 
liquid while it is hot, but becomes solid and jelly-like on 
cooling. 

Two varieties of these substances are described, gelatin 
and chondrin, the latter being derived from cartilages, 
the former from all the other tissues enumerated above, 



12 CHEMICAL COMPOSITION OF HUMAN. BODY. 

and in its purest state, from isinglass, which, is the swim- 
ming bladder of the sturgeon, and which, with the excei^- 
tion of about 7 per cent, of its weight, is wholly reducible 
into gelatin. The most characteristic i^roperty of gelatin 
is that already mentioned, of its solution being liquid when 
warm, and solidifying or setting when it cools. The tem- 
perature at which it becomes solid, the proportion of gela- 
tin which must be in solution, and the firmness of the 
jelly when formed, are various, according to the source, 
the quantity, and the quality of the gelatin ; but, as a 
general rule, one part of dry gelatin dissolved in lOO of 
water, will become solid when cooled to 60°. The solidi- 
fied jelly may be again made liquid by heating it, and the 
transitions from the solid to the liquid state by the alter- 
nate abstraction and addition of heat, may be repeated 
several times ; .but at length the gelatin is so far altered, 
and, apparently, oxydized by the process, that it no longer 
becomes solid on cooling. Gelatin in solutions too weak 
to solidify when cold, is distinguished by being precipitable 
with alcohol, ether, tannic acid, and bichloride of mercury, 
and not precipitable with the ferrocyanide of potassium. 
The most delicate and striking of these tests is the tannic 
acid, which is conveniently supplied in an infusion of oak- 
bark or gall-nuts ; it will detect one part of gelatin in 
5,000 of water; and if the solution of gelatin be strong 
it forms a singularly dense and heavy precipitate, which 
has been named tanno-gelatin, and is completely insoluble 
in water, 

Chondrin, the kind of gelatin obtained from cartilages, 
agrees with gelatin in most of its characters, but its 
solution solidifies on cooling much less firmly, and, unlike 
gelatin, it is precipitable with acetic and the mineral and 
other acids, and with alum, persulphate of iron and acetate 
of lead. 

Albuminous substances, or j^roteids, as they are sometimes 
called, exist abundantly in the human body. The chief 



r 



ALBUMEN. 1 3 

among' tliem are albumen, fibrin, casein, syntonin, mj^osin, 
and globulin. 

Albumen exists in most of the tissues of the body, but 
especially in the nervous, in the lymph, chyle, and blood, 
and in many morbid fluids, as the serous secretions of 
dropsy, pus, and others. In the human body it is most 
abundant, and most nearly pure, in the serum of the blood. 
In all the forms in which it naturally occurs, it is com- 
bined with about six per cent, of fatty matter, phosphate 
of lime, chloride of sodium, and other saline substances. 
Its most- characteristic property is, that both in solution 
and in the half-solid state in which it exists in white-of- 
egg, it is coagulated by heat, and in thus becoming solid, 
becomes insoluble in water. The temperature required 
for the coagulation of albumen is the higher the less 
the proportion of albumen in the solution submitted 
to heat. Serum and such strong solutions will begin to 
coagulate at from 150° to 170°, and these, when the 
heat is maintained, become almost solid and opaque. 
But weak solutions require a much higher temperature, 
even that of boiling, for their coagulation, and either only 
become milky or opaline, or produced flocculi which are 
precipitated. 

Albumen, in the state in whieli it naturally occurs, ap- 
pears to be but little soluble in pure water, but is soluble 
in water containing a small proportion of alkali. In such 
solutions it is probably combined chemically with the 
alkali ; it is i)recipitated from them by alcohol, nitric, and 
other mineral acids, by ferrocyanide of potassium (if before 
or after adding it the alkali combined with the albumen be 
neutralised), by bichloride of mercury, acetate of lead, and 
most metallic salts. 

Coagulated albumen, i.e., albumen made solid with heat, 
is soluble in solutions of caustic alkali, and in acetic acid 
if it be long digested or boiled with it. With the .aid of 
heat, also, strong hydrochloric acid dissolves albumen pre- 



14 CHEMICAL COMPOSITIOX OF HUMAN BODY. 

viously coagulated, and the solution has a beautiful purple 
or blue colour. 

Fibrin is found most abundantly in the blood and the 
more perfect portions of the lymph and chyle. It is very 
doubtful, however, whether fibrin, as such, exists in these 
fluids, — whether, that is to say, it is not itself formed at 
the moment of coagulation. (See Chapter on the Blood.) 

If a common clot of blood be pressed in fine linen while 
a stream of water fiows upon it, the whole of the blood- 
colour is gradually removed, and strings and various pieces 
remain of a soft, yet tough, elastic, and opaque-white sub- 
stance, which consist of fibrin, impure, with a mixture of 
fatty matter, lymph-corpuscles, shreds of the membranes 
of red blood-corpuscles, and some saline substances. Fibrin 
somewhat purer than this may be obtained by stirring blood 
while it coagulates, and collecting the shreds that attach 
themselves to the instrument, or by retarding the coagula- 
tion, and, while the red blood- corpuscles sink, coUecting 
the fibrin unmixed with them. But in neither of these 
cases is the fibrin perfectly pure. 

Chemically, fibrin and albumen can scarcely be distin- 
guished ; the only difi'erence apparently being that fibrin 
contains l*5 more oxygen in every loO parts than albumen 
does. Mr. A. H. Smee has, indeed, apparently cofiverted 
albumen into fibrin, by exposing a solution to the prolonged 
influence of oxygen. Nearly aU the changes, produced by 
various agents, in coagulated albumen, may be repeated 
with coagulated fibrin, with no greater differences of result 
than may be reasonably ascribed to the differences in the 
mechanical properties of the two substances. Of such dif- 
ferences, the principal are, that fibrin immersed in acetic 
acid swells up and becomes transparent like gelatin, while 
albumen undergoes no such apparent change; and that 
deutoxyde of hydrogen is decomposed when in contact with 
coagulated fibrin, but not with albumen. 

Casein, which is said to be albumen in combination with 



SYXTOXIN : MYOSIN. 



15 



soda, exists largely in milk, and forms one of its most im- 
portant constituents. 

Syiitonin is obtained from muscular tissue, both of the 
striated and organic kind. It differs from ordinary fibrin 
in several particulars, especially in being less soluble in 
nitrate and carbonate of potash, and more soluble in dilute 
hydrochloric acid. 

Myosin is the substance which spontaneously coagulates 
in the juice of muscle. It is closely allied to syntonin ; 
indeed, in the act of solution in dilute acid, it is converted 
into it. 

The per-centage composition, of albumen, fibrin, gelatin, 
and chondrin, is thus given by Mulder: — 





Albumen. 


Fibrin. 


Gelatin. 


Chondrin. 


Carbon 

Hydrogen . . 
Nitrogen 

Oxygen . . . 
Sulphur 
Phosphorus . 


53-5 
70 

15-5 

22 

1-6 

0-4 


527 

6-9 

15-4 

23-5 

1-2 
0-3 


50-40 

6-64 

18-34 

1 24-26 


49-97 
6-63 

14-44 
I 28-58 
i 0-38 


• 


100 -Q 


lOO'O 


100 -00 


1 00 -00 



Horny Matter. — The substance of the horny tissues, in- 
cluding the hair and nails (with whale-bone, hoofs, and 
horns), consists of an albuminous substance, with larger 
proportions of sulphur than albumen and fibrin contain. 
Hair contains 10 per cent, and nails 6 to 8 per cent, of 
sulphur. 

The horny substances, to which Simon applied the name 
of keratin, are insoluble in water, alcohol, or ether ; soluble 
in caustic alkalies, and sulphuric, nitric, and hydrochloric 
acids ; and not precipitable from the solution in acids by 
ferrocyanide of potassium. 

Mucus, in some of its forms, is related to these horny 
substances, consisting, in great part, of epithelium detached 



1 6 CHEMICAL COMPOSITION OF HUMAN BODY. 

from the surface of mucous membrane, and floating in a 
peculiar clear and viscid fluid. But under the name of 
mucus, several various substances are included of which 
some are morbid albuminous secretions containing mucus 
and pus-corpuscles, and others consist of the fluid secretion 
variously altered, concentrated, or diluted. Mucus contains 
an albuminous substance, termed mucin. It difiers from 
albumen chiefly in not containing sulphur. 

Pei)sin and other alhuminous fei-ments, as they are some- 
times called, will be described in connection with the secre- 
tions of which they are the active principles. And the 
various colouring matters, as of the blood, bile, &c., will be 
also considered with the fluids or tissues to which they 
belong. 

Besides the above-mentioned organic nitrogenous com- 
pounds, other substances are formed in the living body, 
chiefly by decomposition of nitrogenous materials of the 
food and of the tissues, which must be reckoned rather as 
temporary constituents than essential component parts of 
the body ; although from the continual change, which is a 
necessary condition of life, they are always to be found in 
greater or less amount. Examples of these are urea, uric, 
and hippuric acid, creatin, creatinin, leucin, and many 
others. 

Such are the chief organic substances of which the 
human body is composed. It must not be supposed, how- 
ever, that they exist naturally in a state approaching that 
of chemical purity. All the fluids and tissues of the body 
appear to consist, chemically speaking, of mixtures of 
several of these principles, together with saline matters. 
Thus, for example, a piece of muscular flesh would yield 
fibrin, albumen, gelatin, fatty matters, salts of soda, 
potash, lime, magnesia, iron, and other substances, such as 
creatin, which appear passing from the organic towards 
the inorganic state. This mixture of substances may be 
explained in some measure by the existence of many 



WATER: POTASH; SODA. ij 

different structures or tissues in the muscles ; the gelatin 
may be referred principally to the cellular tissue between 
the fibres, the fatty matter to the adipose tissue in the 
same position, and part of the albumen to the blood and 
the fluid by which the tissue is kept moist. But, beyond 
these general statements, little can be said of the mode in 
which the chemical compounds are united to form an 
organized structure ; or of how, in any organic body, the 
several incidental substances are combined with those 
which are essential. 

The inorganic matters which exist as such in the human 
body are numerous. 

Water forms a large proportion, probably more than 
two-thirds of the weight of the whole body. 

Pliospliorus occurs in combination, — as in the neutral 
phosphate of sodium in the blood and saliva, the acid 
phosphates of the muscles and urine, the basic phosphates 
of calcium and magnesium in the bones and teeth. 

Sulphur is present chiefly in the sulphocyanide of potas- 
sium of the saliva, and in the sulphates of the urine and 
sweat. 

A very small quantity of silica exists, according to 
Berzelius, in the urine, and, according to others, in the 
blood. Traces of it have also been found in bones, in hair, 
and in some other parts of the body. 

Chlorine is abundant in combination with sodium, potas- 
sium, and other bases in all parts, fluid as well as solid, of 
the body. A minute quantity of fluorine in combination 
with calcium has been found in the bones, teeth, and 
urine. 

Potassium and sodium are constituents of the blood and 
all the fluids, in various quantities and proportions. They 
exist in the form of chlorides, sulphates, and phosphates, 
and probably, also, in combination with albumen, or certain 
organic acids. Liebig, in his work on the Chemistry of 
Food, has shown that the juice expressed from muscular 



1 8 CHEMICAL COMPOSITION OF HUMAIS^ BODY. 

flesh always contains a much larger proportion of potash- 
salts than of soda-salts ; while in the blood and other 
fluids, except the milk, the latter salts always preponderate 
over the former; so that, for example, for every lOO parts 
of soda-salts in the blood of the chicken, ox, and horse, 
there are only 40*8, 5*9, and 9-5 parts of potash-salts ; but 
for every lOO parts of soda-salts in their muscles, there 
are 381, 279, and 285 parts of potash-salts. 

The salts of calcium are by far the most abundant of the 
earthy salts found in the human body. They exist in the 
lymph, chyle, and blood, in combination with phosphoric 
acid, the phosphate of calcium being probably held in solu- 
tion by the presence of phosphate of sodium. Perhaps no 
tissue is wholly void of phosphate of calcium; but its 
especial seats are the bones and teeth, in which, together 
with carbonate and fluoride of calcium, it is deposited 
in minute granules, in a peculiar compound, named 
bone-earth, containing 51*55 parts of lime, and 48*45 of 
phosphoric acid. Phosphate of calcium, probably the 
neutral phosphate, is also found in the saliva, milk, bile, 
and most other secretions, and acid phosphate in the urinCy 
and, according to Blondlot, in the gastric fluid. 

Magnesium appears to be always associated with calcium, 
but its proportion is much smaller, except in the juice 
expressed from muscles, in the ashes of which magnesia 
preponderates over lime. 

The especial place of iron is in the haemo-globin, the 
colouring-matter of the blood, of which a further account 
will be given with the chemistry of the blood. Peroxyde 
of iron is found, in very small quantities, in the ashes of 
bones, muscles, and many tissues, and in lymph and chyle, 
albumen of serum, fibrin, bile, and other fluids; and a 
salt of iron, probably a phosphate, exists in considerable 
quantity in the hair, black pigment, and other deeply 
coloured epithelial or homy substances. 

Aluminium, Manganese, Copper, and Lead. — It seems most 



PROTOPLASM. , 19 

likely that in tlie human body, copper, manganesktm, alumi' 
nium, and lead are merely accidental elements, which, being 
taken in minute quantities with the food, and not excreted 
at once with the faeces, are absorbed and deposited in some 
tissue or organ, of which, however, they form no necessary 
part. In the same manner, arsenic, being absorbed, may 
be deposited in the liver and other parts. 



CHAPTER III. 

STKXJCTURAL COMPOSITION OF THE HUMAN BODY. 

In the investigation of the structural composition of the 
human body, it will be well to consider in the first place, 
what are the simplest anatomical elements which enter 
into its formation, and then proceed to examine those 
more complicated tissues which are produced by their 
union. 

It may be premised, that in all the living parts of all 
living things, animal and vegetable, there is invariably to 
be discovered, entering into the formation of their anato- 
mical elements, a greater or less amount of a substance, 
which, in chemical composition and general characters, is 
indistinguishable from albumen. As it exists, in a living 
tissue or orgari, it differs essentially from mere albumen 
in the fact of its possessing the power of growth, develop- 
ment, and the like ; but in chemical composition it is 
identical with it. 

This albuminous substance has received various names 
according to the structures in which it has been found, and 
the theory of its nature and uses which may have pre- 

c 2 



20 STRUCTFEAL COMPOSITION OF HUMAN BODY. 

sented itself most strongly to the minds of its observers. 
In the bodies of the lowest animals, as the Rhizopoda or 
Gregarinida, of which it forms the greater portion, it has 
been called *' sarcode," from its chemical resemblance to the 
flesh of the higher animals. When discovered in vegetable 
cells, and supposed to be the prime agent in their con- 
struction, it was termed " protoplasm." As the presumed 
formative matter in animal tissues it was called '' blastema ;" 
and, with the belief that wherever found, it alone of all 
matters has to do with generation and nutrition, Dr. Beale 
has surnamed it '' germinal matter." 

So far as can be discovered, there is no difference in 
chemical composition betwe.en the protoplasm of one part or 
organism and that of another. The movements which can 
be seen in certain vegetable cells apparently belong to a sub- 
stance which is identical in composition with that which 
constitutes the greater portion of the bodies of the lowest 
animals, and which is present in greater or less quantity 
in all the living parts of the highest. So much appears 
to be a fact ; — that in all living parts there exists an albu- 
minous substance, in which in favourable cases for observa- 
tion in vegetable and the lower animal organisms, there 
can be noticed certain phenomena which are not to be 
accounted for by physical impressions from without, but 
are the result of inherent properties we call vital. For 
example, if a hair of the Tradescantia Virginica, or of 
many other plants, be examined under the microscope, 
there is seen in each individual cell a movement of the pro- 
toplasmic contents in a certain definite direction around the 
interior of the cell. Each cell is a closed sac or bag, and its 
contents are therefore quite cut off from the direct influence 
of any motive power from without. The motion of the 
particles, moreover, in a circuit around the interior of the 
cell, precludes the notion of its being due to any other 
than those molecular changes which we call vital. Again 
in the lowest animals, whose bodies resemble more than 



PEOTOPLASM. 21 

anything else a minute mass of jelly, and wMch. appear 
to be made up almost solely of this albuminous protoplasm, 
there are movements in correspondence with the needs of 
the organism, whether with respect to seizing food 
or any other purpose, which are unaccountable accord- 
ing to any known physical laws, and can only be called 
vital. In many, too, there is a kind of molecular cur- \' 
rent, exactly resembling that which is seen in a vegetable \ 
ceU. 

In the higher animals, phenomena such as these are so 
subordinate to the more complex manifestations of life that 
they are apt to be overlooked ; but they exist nevertheless. 
The mere nutrition of each part of the body in man or in 
the higher animals, is performed after a fashion which is 
strictly analogous to that which holds good in the case of 
a vegetable cell, or a rhizopod ; or, in other words, the 
life of each anatomical element in a complex structure, 
like the human body, resembles very closely the life of 
what in the lowest organisms constitutes the whole being. 
For example, the thin scaly covering or epidermis, which 
forms the outer part of a man's skin, is made up of minute 
cells, which, when living, are composed in part of pro- 
toplasm, and which are continually wearing away and 
being replaced by new similar elements from beneath ; 
and this process of quick waste and repair could only take 
place under the very complex conditions of nutrition which 
exist in man. One working part of the organism of an 
animal is so inextricably interwoven with that of another, 
that any want or defect in one, is soon or immediately felt 
by the whole ; and the epidermis, which only subserves a 
mechanical function, would be altered very soon by any 
defect in the more essential parts concerned in circulation, 
respiration, &c. But if we take simply the life-history 
of one of the small cells which constitute the epidermis, 
we find that it absorbs nourishment from the parts around, 
grows, and developes in a manner analogous to that which 



22 STEUCTUEAL COMPOSITION OF HUMAN BODY. 

belongs to a cell whicli constitutes part of a vegetable 
structure, or even a cell wbicli by itself forms an indepen- 
dent being. 

llemembering, however, the invariable presence of a 
living albuminous matter or protoplasm of apparently 
identical composition in all living tissues, animal and 
vegetable, we must not forget that its relations to the 
parts with which it is incorporated are still very doubtfully 
known ; and all theories concerning it must be considered 
only tentative and of uncertain stability. 

Among the anatomical elements of the human body, 
some appear, even with the help of the best microscopic 
apparatus, perfectly uniform and simple : they show no trace 
of structure, i.e., of being composed of definitely arranged 
dissimilar parts. These are named simple, structureless, or 
amorphous substances. Such is the simple membrane which 
forms the walls of most primary cells, of the finest gland- 
ducts, and of the sarcolemma of muscular fibre ; and such 
is the membrane enveloping the vitreous humour of the 
eye. Such also, having a dimly granular appearance, 
but no really granular structure, is the intercellular sub- 
stance of the so-called hyaline cartilage. 

In the parts which present determinate structure, certain 
primary forms may be distinguished, which, by their 
various modifications and modes of combination make up 
the tissues and organs of the body. Such are, i. Gra- 
nules or molecules, the simplest and minutest of the primary 
forms. They are particles of various sizes, from immea- 
surable minuteness to the 10,000th of an inch in diameter; 
of various and generally uncertain composition, but usually 
so affecting light transmitted through them, that at dif- 
ferent focal distances their centre, or margin, or whole 
substance, appears black. From this character, as well as 
from their low specific gravity (for in microscopic examina- 
tions they always appear lighter than water), and from 
their solubility in ether when they can be favourably 



NUCLEI. 23 

tested, it is probable that most granules are formed of 
fatty or oily matter ; or, since they do not coalesce as 
minute drops of oil would, that they are particles of oil 
coated over with albumen deposited on them from the 
fluid in which they float. In any fluid that is not too 
viscid, they exhibit the phenomenon of molecular motion, 
shaking and vibrating incessantly, and sometimes moving 
through the fluid, probably, in great measure, under the 
influence of external vibration. 

Granules may be either free, as in milk, chyle, milky 
serum, yelk-substance, and most tissues containing cells 
with granules; or enclosed, as are the granules in 
nerve-corpuscles, gland-cells, and epithelium- cells, the 
pigment granules in the pigmentum nigrum and me- 
dullary substance of the hair; or imbedded, as are the 
granules of phosphate and carbonate of lime, in bones and 
teeth. 

2. Nuclei, or cytoblasts (fig. i, &), appear to be the simplest 
elementary structures, next to granules. They were thus 
named in accordance with the hypothesis that they are 
always connected with cells, or tissues formed from cells, 
and that in the development of these, each nucleus is the 
germ or centre around which the cell is formed. The 
hypothesis is only partiaUy true, but the terms based on it 
are too familiarly accepted to make it advisable to change 
them till some more exact and comprehensive theory is 
formed. 

Of the corpuscles called nuclei some are minute cellules 
or vesicles, with walls formed of simple membrane, enclos- 
ing often one or more particles, like minute granules, 
called nucleoli (fig. i, c). Other nuclei, again, appear to 
be simply small masses of protoplasm, with no trace of 
vesicular structure. 

One of the most general characters of the nucleus, and 
the most useful in microscopic examinations, is, that it is 
neither dissolved nor made transparent by acetic acid, but 



24 STEUCTUEAL COMPOSITION OF HUMAN EODY. 

acquires, when that fluid is in contact with it, a darker and 
more distinct outline. It is commonly, too, the part of the 
mature cell which is capable of being stained by an ammo- 
niacal solution of carmine — the test, it may be remarked, 
by which, according to Dr. Beale, protoplasm or germinal 
matter may be always known. 

Nuclei may be either free or attached. Free nuclei are 
such as either float in fluid, like those in some of the secre- 
tions, which appear to be derived from the secreting cells 
of the glands, or lie loosely embedded in solid substance, as 
in the grey matter of the brain and spinal cord, and most 
abundantly in some quickly-growing tumours. Attached 
nuclei are either closely imbedded in homogeneous pellucid 
substance, as in rudimental cellular tissue ; or are fixed on 
the surface of fibres, as on those of organic muscle and 
organic nerve-fibres ; or are enclosed in cells, or in tissues 
formed by the extension or junction of cells. Nuclei en- 
closed in cells appear to be attached to the inner surface of 
the ceU-wall, projecting into the cavity. Their position in 
relation to the centre or axis of the cell is uncertain ; often 
when the cell lies on a flat or broad surface, they appear 
central, as in blood corpuscles, epithelium-cells, whether 
tesselated or cylindrical; but, perhaps, more often their 
position has no regular relation to the centre of the cell. 
In most instances, each cell contains only a single nucleus; 
but in cartilage, especially when it is growing or ossifying, 
two or more nuclei in each cell are common; and the 
development of new cells is often efi'ected. by a division or 
multiplication of nuclei in the cavity of a parent cell ; as in 
the primary blood-cells of the embryo in the germinal 
vesicle, and others. 

When ceUs extend and coalesce, so that their walls form 
tubes or sheaths, the nuclei commonly remain attached to 
the inner surface of the wall. Thus they are seen imbedded 
n the walls of the minutest capillary blood-vessels of, for 
example, the retina and brain ; in the sarcolemma of 



CELLS. 



25 



transversely striated muscular fibres ; and in minute gland- 
tubes. 

Nuclei are most commonly oval or round, and do not 
generally conform themselves to tbe diverse shapes which 
the cells assume; they are altogether less variable ele- 
ments, even in regard to size, than the cells are, of which 
fact one may see a good example in the uniformity of the 
nuclei in cells so multiform as those of epithelium. But 
sometimes they appear to be developed into filaments, 
elongating themselves and becoming solid, and uniting 
end to end for greater length, or by lateral branches to 
form a network. So, according to Henle, are formed the 
filaments of the striated and fenestrated coats of arteries ; 
and, according to Beale, the so-called connective tissue cor- 
puscles are to be considered branched nuclei, formed of 
protoplasm or germinal matter. 

3. Cells. — The word '' cell " of course implies strictly a 
hollow body, and the term was a sufficiently good one 
when all so-called cells were considered to be small bags 
with a membranous envelope, and more or less liquid 
contents. Many bodies, however, which are still called 
ceUs do not answer to this description, and the term, there- 
fore, if taken in its literal signification, is very apt to lead 
astray, and, indeed, very frequently does so. It is too 
widely used, however, to be given up, at least for the 
present, and we must therefore consider the term to indi- 
cate, either a membranous closed bag with more or less liquid 
contents, and almost always a nucleus ; or a small semi- 
solid mass of protoplasm, with no more definite boundary- 
wall than such as has been formed by a condensation of its 
outer layers, but with, most commonly, a small granular 
substance in the centre, called, as in the first place, a 
nucleus. In both cases the nucleus may contain a nucleolus. 
Fat cells (fig. 11) are examples of the first kind of cells ; 
white blood-corpuscles (fig. 26^ of the second. 

The cell- wall, when there is one, never presents any 



26 STRUCTURiiX COMPOSITIOX OF HUMAN BODY. 

appearance of structure : it appears sometimes to be an 
albuminous substance; sometimes a horny matter, as in 
thick and dried cuticle. In almost all cases (the dry cells of 
homy tissue, perhaps, alone excepted) the cell- wall is made 
transparent by acetic acid, which also penetrates into the 
interior and distends it, so that it can hardly be discerned. 
But in such cases the cell-wall is usually not dissolved ; it 
may be brought into view again by merely neutralizing 
the acid with soda or potash. 

The simplest sJiape of cells, and that which is probably 
the normal shape of the primary cell, is oval or spheroidal, 
as in cartilage-cells and lymph- corpuscles ; but in many in- 
stances they are flattened and discoid, as in the red blood- 
corpuscles (fig. 26) or scale-like, as in the epidermis and 
tesselated epitheKum (fig. 2). By mutual pressure they 
may become many-sided, as are most of the pigment-cells 
of the choroidal pigmentum nigrum (fig. 12), and those 
in close-textured adipose tissue ; they may assume a conical 
or cylindriform or prismatic shape, as in the varieties of 
cylinder-epithelium (fig. 4) ; or be caudate, as in certain 
bodies in the spleen ; they may send out exceedingly fine 
processes in the form of vibratile cilia (fig. 6), or larger 
processes, with which they become stellate, or variously 
caudate, as in some of the ramified pigment-cells of the 
choroid coat of the eye (fig. 13). 

The contents of all living cells, including the nucleus, are 
formed in a greater or less degree of protoplasm, — less as 
the cell grows older. But, besides, cells contain matters 
almost infinitely various, according to the position, office, 
and age of the cell. In adipose tissue they are the oily 
matter of the fat ; in gland-cells, the contents are the 
proper substance of the secretion, bile, semen, &c., as the 
case may be ; in pigment-cells they are the pigment-gra- 
nules that give the colour ; and in the numerous instances 
in which the cell-contents can be neither seen because they 
are pellucid, nor tested because of their minute quantity, 



IXTERCELLULAE SUBSTANCE. 



27 



they are yet, probably, peculiar in each tissue, and con- 
stitute the greater part of the proper substance of each. 
Commonly, when the contents are pellucid, they contain 
granules which float in them ; and when water is added 
and the contents are diluted, the granules display an active 
molecular movement within the cavity of the cell. Such 
a movement may be seen by adding water to mucus-, or 
granulation-corpuscles, or to those of lymph. In a few 
cases, the whole cavity of the cell is fiUed with granules : 
it is so in yelk-cells and milk-corpuscles, in the large 
diseased corpuscles often found among the products of 
inflammation, and in some ceUs when they are the seat of 
extreme fatty degeneration. AU cells containing abundant 
granules appear to be either lowly organized, as for nutri- 
ment, e.g., yelk-cells, or degenerate, e.g., granule-cells of 
inflammation, or of mucus. The peculiar contents of cells 
may be often observed to accumulate first around or di- 
rectly over the nuclei, as in the cells of black pigment, in 
those of melanotic tumours, and in those of the liver during 
the retention of bile. 

Intercellular' substance is the material in which, in certain 
tissues, the cells are imbedded. Its quantity is very 
variable. In the finer epithelia, especially the columnar 
epithelium on the mucous membrane of the intestines, it 
can be just seen filling the interstices of the close-set cells; 
here it has no appearance of structure. In cartilage and 
bone, it forms a large portion of the whole substance of 
the tissue, and is either homogeneous and finely granidar 
(fig. 14), or osseous, or, as in fibro-cartilage, resembles fine 
fibrous tissue (fig. 15). In some cases, the cells are very 
loosely connected with the intercellular substance, and may 
be nearly separated fi:om it, as in fibro-cartilage : but in 
some their waUs seem amalgamated with it. 

The foregoing may be regarded as the simplest, and the 
nearest to the primary forms assumed in the organization 
of animal matter j as the states into which this passes in 



28 STRUCTURAL COMPOSITIOX OF HUMAN BODY. 

becoming a solid tissue living or capable of life. By the 
further development of tissue thus far organized, higher or 
secondary forms are produced, which it will be sufficient in 
this place merely to enumerate. Such are, 

4. Filaments, ox Jihrils. — Threads of exceeding fineness, 
firom ^— -U^th of an inch upwards. Such filaments are 
cylindriform, as are those of the striated muscular and 
the fibro-cellular or areolar tissue (fig. 8) ; or flattened, as 
are those of the organic muscles. Filaments usually lie 
in parallel fasciculi, as in muscular and tendinous tissues ; 
but in some instances are matted or reticular with branches 
and intercommunication, as are the filaments of the middle 
coat, and of the longitudinally-fibrous coat of arteries ; and 
in other instances, are spirally wound, or very tortuous, as 
in the common fibro-cellular-tissue (fig. 9) . 

5 . Fibres in the instances to which the name is commonly 
applied are larger than filaments or fibrils, but are by no 
essential general character distinguished from them. The 
flattened band-like fibres of the coarser varieties of organic 
muscle or elastic tissue (fig. 10) are the simplest examples 
of this form ; the toothed fibres of the crystalline lens are 
more complex ; and more compound, so as hardly to permit 
of being classed as elementary forms, are the striated mus- 
cular fibres, which consist of bundles of filaments enclosed 
in separate membranous sheaths, and the cerebro-spinal 
nerve-fibres, in which similar sheaths enclose apparently 
two varieties of nerve substance. 

6. Tubules are formed of simple, or structureless mem- 
brane, such as the investing sheaths of striated muscular 
and cerebro-spinal nerve-fibres, and the basement mem- 
brane or proper wall of the fine ducts of secreting glands ; 
or they may be formed, as in the case of the minute capil- 
lary lymph and blood-vessels, by the apposition, edge to 
edge, in a single layer, of variously shaped flattened cells 

(fig. 48). 

AVith these simple materials, the various parts of the 



f 



EPITHELIUM. 



29 



body are built up ; the more elementary tissues being, so 
to speak, first compounded of them; while these again 
are variously mixed and interwoven to form more intricate 
combinations. Thus are constructed epithelium and its 
modifications, connective tissue, fat, cartilage, bone, the 
fibres of muscle and nerve, etc. ; and these again, with the 
more simple structures before mentioned, are used as mate- 
rials wherewith to form arteries, veins, and lymphatics, 
secreting and vascular glands, lungs, heart, liver, and other 
parts of the body. 



CHAPTER IV.^^ 

STRUCTURE OF THE ELEMENTARY TISSUES. 

Epithelium. 

One of the simplest of the elementary structures of which 
the human body is made up, is that which has received the 
name of Epithelium. Composed of nucleated cells which are 
arranged most commonly in the form of a continuous 
membrane, it lines the free surfaces both of the inside and 
outside of the body, and its varieties, with one exception, 
have been named after the shapes which the individual 
cells in different parts assume. Classified thus, Epithelium 
presents itself under four principal forms, the characters 
of each of which are distinct enough in well-marked ex- 
amples; but when, as frequently happens, a continuous 



* The following Chapter, containing an outline-description of the 
elementary tissues, has been inserted for the convenience of students. 
For a much fuller and better account, the reader may be referred to 
Dr. Sharpey's admirable descriptions in Quain's Anatomy. 



JO 



ELEMENTARY TISSUES. 



surface possesses at different parts two or more different 
epithelia, there is a very gradual transition from one to tlie 
other. 

I. The first and most common variety is the squamous 
or tesselated epithelium (figs. I and 2), which is composed 
of flat, oval, roundish, or polygonal nucleated cells, of 
various size, arranged in one, or in many superposed 
layers. Arranged in several superposed layers this form of 

Fig. I* Fig. 2.+ 




epithelium covers the skin, where it is called the Epidermis y 
and is spread over the mouth, pharynx, and oesophagus, 
the conjunctiva covering the eye, the vagina, and entrance 
of the urethra in both sexes ; while, as a single layer the 
same kind of epithelium lines the interior of most of the 
serous and synovial sacs, and of the heart, blood-vessels, 
and lymph- vessels. 

2. Another variety of epithelium named spheroidal, from 
the usually more or less rounded outline of the cells com- 



* Fig. I. Fragment of ex^ithelimn from a serous membrane (peri- 
toneum) ; magnified 410 diameters, a. cell ; h. nucleus ; c. nucleoli 
(Henle). 

t Fig. 2. Epithelium scales from the inside of the mouth ; magnified 
260 diameters (Henle). 



EPITHELIUM. 



31 



posing it {d, fig. 3), is found chiefly lining the interior of the 
ducts of the compound glands, and more or less completely 
filling the small sacculations or acini, in which they ter- 
minate. It commonly indeed occupies the true secreting 
parts of all glands, and hence is sometimes called glandular 
epithelium {b, c, and ti, fig. 3). Often, from mutual pressure^ 




the cells acquire a polygonal outline. From the fact, how- 
ever, of the term spheroidal epithelium being a generic one 
for almost all gland-cells, the shapes and sizes of the cells 
composing this variety of epithelium are, as might be ex- 
pected, very diverse in different parts of the body. 

3. The third variety is the cylindrical or columnar 



* Fig. 3. The gastric glands of the human stomach (magnified). 
a, deep part of a pyloric gastiic gland (from KoUiker) ; the cylindrical 
epitheliimi is traceable to the crecal extremities, h and c, cardiac 
gastric glands (from Allen Thomson) ; h, vertical section of a small 
portion of the mucous membrane with the glands magnified 30 diameters ; 
c, deeper portion of one of the glands, magnified 65 diameters, showing 
a slight division of the tubes, and a sacculated appearance produced by 
the large glandidar cells within them ; d, cellular elements of the cardiac 
glands magnified 250 diameters. 



32 



ELEMEXTARY TISSUES. 



epitlielium (figs. 4 and 5), whicli extends from the cardiac 
orifice of the stomach along the whole of the digestive 
canal to the anus, and lines the principal gland-ducts which 

Fi^. 4.* 




open upon the mucous surface of this tract, sometimes 
throughout their whole extent {a, fig. 3), but in some cases 
only at the part nearest to the orifice (6 and c) . It is also 

Fiq. 5.t 




found in the gall-bladder and in the greater portion of the 
urethra, and in some other parts, as the duct of the parotid 
gland and of the testicle. It is composed of oblong cells 
closely packed, and placed perpendicularly to the surface 
they cover, their deeper or attached extremities being most 



* Fig. 4. Cylindrical epitlielium from intestinal villus of a rabbit ; 
magnified 300 diameters (from KoUiker). 

t Fig. 5. Cylinders of the intestinal epithehum (after Henle) : — 
B. from the jejunum ; c. cyhnders of the intestinal epithelium as 
seen Avhen looking on their free extremities ; d. ditto, as seen on a 
transverse section of a villus. 



EPITHELIUM. 



33 



commonly smaller than those which are free. Each of such 
cells encloses^ at nearly mid distance between its base and 
apex, a flat nucleus with nucleoli (b, fig. o) ; the nuclei 
being arranged at such heights in contiguous cells as not 
to interfere with each other by mutual pressure. 

4. The fourth variety of epithelium cells, usually 
cylindrical, but occasionally of some other shape, are pro- 
vided at their free extremities with several fine pellucid 
pliant processes or cilia (figs. 6 and 7). This form of epi- 
thelium lines the whole respiratory tract of mucous mem- 
brane and its prolongations. It occurs also in some parts 



Fig. 6.* 



Fig. 7-1 





of the generative aj^paratus ; in the male, lining the vasa 
efferentia of the testicle, and their prolongations as far as 
the lower end of the epididymis ; and, in the feniale com- 
mencing about the middle of the neck of the uterus, and ex- 
tending to the fimbriated extremities of the Fallopian tubes, 
and for a short distance along the peritoneal surface of the 
latter. A tesselated epithelium, with scales partly covered 
with cilia, lines, in great part, the interior of the cerebral 
ventricles. 

If a portion of ciliary mucous membrane from a living or 
recently dead animal be moistened and examined with a 
microscope, the cilia are observed to be in constant motion, 



* Fig. 6. Si^heroidal ciliated cells from the moutli of the frog ; 
magnified 300 diameters (Sharpey), 

t Fig. 7. Columnar ciliated epithelium cells from the human nasal 
membrane ; magnified 300 diameters (Sharpey). 



34 ELEMEXTARY TISSUES. 

moving continually back-vrards and forwards, and alter- 
nately rising and falling with a lashing or fanning 
movement. The appearance is not unlike that of the 
waves in a field of com, or swiftly running and rippling 
water. The general result of their movements is to pro- 
duce a continuous current in a determinate direction, and 
this direction is invariably the same on the same surface, 
being usually in the case of a cavity towards its external 
orifice. 

Uses of Epithelium. — The various kinds of epithelium 
serve one general purpose, namely, that of protecting, and 
at the same time rendering smooth, the surfaces on which 
they are placed. But each, also, discharges a special office 
in relation to the particular function of the membrane on 
which it is placed. 

In mucous and synovial membranes it is highly probable 
that the epithelium-cells, whatever be their forms and what- 
ever their other functions, are the organs in which by a 
regular process of elaboration and secretion, such as will be 
afterwards described, mucus and synovial fluid are formed 
and discharged. (See chapter on Secretion). 

Ciliated epithelium has another superadded function. By 
means of the current set up by its cilia in the air or fluid 
in contact with them, it is enabled to propel the fluids 
or minute particles of solid matter, which come within 
the range of its influence, and aid in their expulsion 
from the body. In the respiratory tract of mucous mem- 
brane the current set up in the air may also assist in 
the diffusion and change of gases, on which the due 
aeration of the blood depends. In the Fallopian tube 
the direction of the current excited by the cilia is towards 
the cavity of the uterus, and may thus be of service in 
aiding the progress of the ovum. Of the purposes served 
by the cilia which line the ventricles of the brain nothing 
is known. 

The nature of ciliary motion and the circumstances by 



AEEOLAR TISSUE. 35 

which it is influenced will be considered hereafter. (See 
chapter on Motion.) 

Epithelium is devoid of blood-vessels, and lymphatics. 
The cells composing it are nourished by absorption of 
nutrient matter from the tissues on which they rest ; and 
as they grow old they are cast off and replaced by new cells 
from beneath. 

Areolar, Cellular, or Connective Tissue. 

This tissue, which has received various names according 
to the qualities which seemed most important to the authors 
who have described it, is met with in some form or other in 
every region of the body ; the areolar tissue of one dis- 
trict being, directly or indirectly, continuous with that of 

Firj. 8.* 




all others. In most parts of the body this structure 
contains fat, but the quantity of the latter is very variable, 
and in some few regions it is absent altogether (p. 38). 



* Fig. 8. Filaments of areolar tissue, in larger and smaller bundles, 
as seen under a magnifying power of 400 diameters (Sharpey). 

D 2 



36 



ELEMEXTARY TISSUES. 



Probably no nerves are distributed to areolar tissue itself, 
although they pass through it to other structures; and 
although blood-vessels are supplied to it, yet they are 
sparing in quantity, if we except those destined for the fat 
which is held in its meshes. 

Under the microscope areolar tissue seems composed of 
a mesh- work of fine fibres of two kinds. The first, which 
makes up the greater part of the tissue, is formed of very 
fine white structureless fibres, arranged closely in bands and 
bundles, of wave-like appearance when not stretched out, 
and crossing and intersecting in all directions (fig. 8). The 
second kind, or the yeUow elastic fibre (fig. lo), has a much 

Fig. 9.* 




sharper and darker outline, and is not arranged in bundles, 
but intimately mingled with the first variety, as more or 
less separate and well-defined fibres, which twist among and 
around the bundles of white filaments (fig. 9). Sometimes 



* Fig. 9. Magnified view of areolar tissues (from different jmrts) 
treated with acetic acid. The white filaments are no longer seen, and 
the yellow or elastic fibres Avith the nuclei come into view. At c, 
elastic fibres wind round a bundle of white fibres, which, by the efi'ect 
of the acid, is swollen out between the turns. Some connective tissue 
corpuscles are indistinctly represented in c (Sharpey). 



AREOLAR TISSUE. 



37 



Fig. lo.* 



the yellow fibres divide at their ends and anastomose with 
each other by means of the branches. Among the fibrous 
parts of areolar or connective tissue are little nuclear 
bodies of various shapes, called connective-tissue corpuscles 
(fig. g, c), some of which are prolonged at various points 
of their outline into small processes which meet and join 
others like them proceeding from their neighbours. 

The chief functions of areolar tissue seem to consist in 
the investment and mechanical support of various parts, 
and as a connecting bond between such structures as may 
need it. The connective-tissue corpuscles, which, accord- 
ing to Beale, are small branched particles of germinal 
matter or protoplasm, probably minister to the nutrition of 
the texture in which they are seated. 

In various parts of the body, 
each of the two constituents of 
areolar tissue which have been 
just mentioned, may exist sepa- 
rately, or nearly so. Thus ten- 
dons, fascia), and the like more 
or less inelastic structures, are 
formed almost exclusively of the 
white fibrous tissue, arranged ac- 
cording to the purpose required, 
either in parallel bundles or 
membraneous meshes ; while the 
yellow elastic fibres are found to 
make up almost alone such elas- 
tic structures as the vocal cords, 
the ligamenta subflava, etc., and 
to enter largely into the composition of the blood-vessels, 
the trachea, the lungs, and many other parts of the body. 




* Fig. lo. Elastic fibres from the ligamenta subflava, magnified 
about 200 diameters (Sharpey). 



3« 



ELEMEXTAEY TISSUES. 



Adipose Tissue. 

In almost all regions of the human body a larger or 
smaller quantity of adipose or faWj tissue is present ; the 
chief exceptions being the subcutaneous tissue of the eye- 
lids, penis and scrotum, the nymphee and the cavity of 
the cranium. Adipose tissue is also absent from the sub- 
stance of many organs, as the lungs, liver and others. 

Fatty matter, not in the form of a distinct tissue, is also 
widely present in the body, as the fat of the liver and 
brain, of the blood and chyle, etc. 

Adipose tissue is almost always found seated in areolar 
tissue, and forms in its meshes little masses of unequal 
size and irregular shape, to which the term, lobules, is 
commonly applied. Under the microscope it is found to 




consist essentially of little vesicles or cells about ^{^th or 
■s^-o-tlj- of an inch in diameter, each composed of a struc- 
tureless and colourless membrane or bag, filled with fatty 
matter which is liquid during life, but in part solidified 
after death. A nucleus is always present in some part or 
other of the cell-waU ; but in the ordinary condition of the 

* Fig. II. A small cluster of fat-cells; magnified 150 diameters 
(Sharpey). 



riGMENT-CELLS. 39 

cell it is not easily or always visible. The ultimate cells are 
held together by capillary blood-vessels; while the little 
clusters thus formed are grouped into small masses, and 
held so, in most cases, by areolar tissue. The oily matter 
contained in the cells is composed chiefly of the compounds 
of fatty acids with glycerin, which are named olein, stearin, 
and palmitin. 

It is doubtful whether lymphatics or nerves are supplied 
to fat, although both pass through it on their way to other 
structures. 

Among the uses of fat, these seem to be the chief : — 

1. It serves as a store of combustible matter which 
may be re-absorbed into the blood when occasion re- 
quires, and being burnt, may help to preserve the heat of 
the body. 

2. That part of the fat which is situate beneath the skin 
must, by its want of conducting power, assist in preventing 
undue waste of the heat of the body by escape from the 
surface. 

3. As a packing material, fat serves very admirably to 
fill up spaces, tj form a soft and yielding yet elastic mate- 
rial wherewith to wrap tender and delicate structures, or 
form a bed with like qualities on which such structures 
may lie, unendangered by pressure. As good examples of 
situations in which fat serves such purposes may be men- 
tioned the palms of the hands, and soles of the feet, and 
the orbits. 

4. In the long bones, fatty tissue, in the form known as 
marrow, serves to fill up the medullary canal, and to sup- 
port the small blood-vessels which are distributed from it 
to the inner part of the substance of the bone. 

Pigment. 

In various parts of the body there exists a considerable 
quantity of dark pigmentary matter, e.g., in the choroid 
coat of the eye, at the back of the iris, in the skin, etc. 



40 



ELEMENTARY TISSUES. 



In all these eases the dark colour is due to the presence of 
so-called pigment- cells. 

Pigment- cells are for the most part polyhedral (fig. 12) 
or spheroidal, although sometimes they have irregular 
processes, as shown in fig. 13. The cell-wall itself is 
colourless, — the dark tint being produced by small dark 
granules heaped closely together, and more or less con- 
cealing the nucleus, itself colourless, which each cell 
contains. The dark tint of the skin, in those of dark com- 
plexion and in the coloured races, is seated chiefly in the- 



Fig. 12. 



-?%. i3-t 





epidermis, and depends on the presence of pigment- cells,. 
which, except in the presence of the dark granules in their 
interior, closely resemble the colourless cells with which 
they are mingled. The pigment-cells are situate chiefly in 
the deep layer of the epidermis, or the so-called rete- 
mucosum. (See chapter on the Skin.) 



* Fig. 12. Pigment-cells from the clioroid ; magnified 370 diameters 
(Henle). A, cells still cohering, seen on their surface ; a, nucleus 
indistinctly seen. In the other cells the nucleus is concealed by the 
];)igment granules. B, two cells seen in profile ; a, the outer or posterior 
part containing scarcely any pigment. 

+ Fig. 13. Eamified pigment cells^, from the tissue of the choroid 
coat of the eye ; magnified 350 diameters (after Kolliker). a, cells with 
pigment ; &, colourless fusiform cells. 



CARTILAGE. 4I 

The pigmentary matter is a very insoluble compound 
of carbon, hydrogen, nitrogen and oxygen, — the carbon 
largely predominating ; besides, there is a small quantity 
of saline matter. 

The uses of pigment in most parts of the body are not 
clear. In the eyeball it is evidently intended for the 
absorption of superfluous rays of light. 

Cartilage. 

Cartilage or gristle exists in different forms in the 
human body, and has been classified under two chief 
heads, namely, temporary and permanent cartilage ; the 
former term being applied to that kind of cartilage which, 
in the foetus and in young subjects, is destined to be con- 
verted into bone. The varieties of permanent cartilage 
have been arranged in three classes, namely, the cellular, 
the hyaline, and the fibrous cartilages, — the last-named, 
being again capable of subdivision into two kinds, 
namely, elastic or yellow cartilage, and the so-called fibro- 
cartilage. 

Elastic cartilage, however, contains fibres, and fibro- 
cartilage is more or less elastic ; it will be well, therefore, 
for distinction's sake to term those two kinds uliite fibro- 
cartilage and yellow fibro-cartilage respectively. 

The accompanying table represents the classification of 
the varieties of cartilage : — 

1. Temporary. 

( A. CeHular. 

2. Permanent. \ ^' ^y^^^^^- , ,.., . ., ., 

) n T?,-T,^^„-. J vV lute fiDro-cai-tilaf'c. 
( <^-Fi^^o^^s. I Yellow fibro-cartilage. 

All kinds of cartilage are composed of cells imbedded 
in a substance called the matrix : and the apparent 
differences of structure met with in the various kinds of 
cartilage are more due to differences in the character of 
the matrix than of the cells. Among the latter, however, 
there is also considerable diversity of form and size. 



42 



ELEMENTARY TISSUES. 



With the exception of the articular variety, cartilage is 
invested by a thin but tough and firm fibrous membrane 
called the perichondrium. On the surface of the articular 
cartilage of the foetus, the perichondrium is represented by 
a film of epithelium ; but this is gradually worn away up 
to the margin of the articular surfaces, when by use the 
parts begin to suffer friction. 

I . Cellular cartilage may be readily obtained from the 
external ear of rats, mice, or other small mammals. It is 
composed almost entirely of cells (hence its name), with little 
or no matrix. The latter, when present, consists of very fine 
fibres, which twine about the cells in various directions and 
enclose them in a kind of network. The cells are packed 
very closely together,— so much so that it is not easy in all 
cases to make out the fine fibres often encircling them. 
Cellular cartilage is found in the human subject, only 

in early foetal life, when it 
constitutes the Chorda dor- 
salis. (See chapter on Genera- 
tion.) 

,.- 2. Hyaline cartilage is met 
with largely in the human 
body, — investing the articular 
ends of bones, and forming 
the costal cartilages, the nasal 
cartilages, and those of the 
larjTix, with the exception of 
the epiglottis and cornicula 
laryngis. Like other cartilages it is composed of cells 
imbedded in a ynatrix (fig. 14). 




* Fig. 14. A tliin layer peded off from the surface of the cartilage 
of the head of the humeras, showing flattened gi'oups of cells. The 
shrunken cell-bodies are distinctly seen, but the limits of the capsular 
cavities, where they adjoin one another, are but faintly indicated. 
Magnified 400 diameters (after Sharx)ey). 



CARTILAGE. 43 

The cells, whicli contain a nucleus with, nucleoli, are 
irregular in shape, and generally grouped together in 
patches. The patches are of various shapes and sizes, and 
j)laced at unequal distances apart. They generally appear 
flattened near the free surface of the mass of cartilage in 
which they are x^laced, and more or less perpendicular to 
the surface in the more deeply seated portions. 

The matrix in which they are imbedded has a dimly 
granular appearance, like that of ground glass. 

In the hyaline cartilage of the ribs, the cells are mostly 
larger than in the articular variety, and there is a tendency 
to the development of fibres in the matrix. The costal 
cartilages also frequently become ossified in old age, as 
also do some of those of the larynx. 

Temporary cartilage closely resembles the ordinary 
hyaline kind ; the cells, however, are not grouped together 
after the fashion just described, but are more uniformly 
distributed throughout the matrix. 

Articular hyaline cartilage is reckoned among the so- 
called non-vascular structures, no blood-vessels being sup> 
plied directly to its own substance; it is nourished by 
those of the bone beneath. When hyaline cartilage is in 
thicker masses, as in the case of the cartilages of the ribs, 
a few blood-vessels traverse its substance. The distinction, 
however, between all so-called vascular and non-vascular 
j)arts, is at the best a very artificial one. (See chapter on 
Nutrition.) 

Nerves are probably not supplied to any variety of 
cartilage. 

Fibrous cartilage, as before mentioned, occurs under two 
chief forms, the yellow and the white fibro-cartilage. 

Yellow fibro-cartilage is found in the external ear, in the 
epiglottis and cornicula laryngis, and in the eyelid. The 
cells are rounded or oval, with well-marked nuclei and 
nucleoli. The matrix in which they are seated is composed 
almost entirely of fine fibres, which form an intricate inter- 




44 ELEMENTARY TISSUES. 

lacement about the cells, and in their general characters 
are allied to the yellow variety of fibrous tissue (fig. 15). 

„ . ^ White fibro-cartila^e, which 

IS much more wideh^ distri- 
buted throughout the body, 
than the foregoing kind, is 
composed, like it, of cells and 
a matrix; the latter, however, 
being made up almost entirely 
of fibres closely resembling 
those of white fibrous tissue. 
In this kind of fibro-car- 
tilage it is not unusual to find a great part of its mass 
composed almost exclusively of fibres, and deserving the 
name of cartilage only from the fact that in another por- 
tion, continuous wdth it, cartilage cells may be pretty freely 
distributed. 

The difi'erent situations in which white fibro-cartilage is 
formed have given rise to the following classification : — 

1. Inter-articular fibro-cartilage, e.g., the semilunar car- 
tilages of the knee-joint. 

2. Circumferential or marginal, as on the edges of the 
acetabulum and glenoid cavity of the scapula. 

3. Connecting, e.g., the inter-vertebral fibro-cartilages. 

4. Fibro-cartilage is found in the sheaths of tendons, 
and sometimes in their substance. In the latter situation, 
the nodule of fibro-cartilage is called a sesamoid fibro-carti- 
lage, of which a specimen may be found in the tendon of 
the tibialis posticus, in the sole of the foot, and usually in 
the neighbouring tendon of the peroneus longus. 

The uses of cartilage are the following : — in the joints, 
to form smooth surfaces for easy friction, and to act as a 
huffer, in shocks ; to bind bones together, yet to allow a 
certain degree of movement, as between the vertebras ; to 

* Fig. 15. Section of the epiglottis, magnified 380 diameters (Dr. 
Baly). 



BOXE. 45 

form a firm framework and protection, yet without undue 
stiffness or weight, as in the larynx and chest walls ; to 
deepen joint-cavities, as in the acetabulum, yet not so as 
to restrict the movements of the bones ; to be, where such 
qualities are required, firm, tough, flexible, elastic, and 
strong. 

Structure of Bones and Teeth. 

Bone is composed of earthy and animal matter in the 
proportion of about 6/ per cent, of the former to 33 per 
cent, of the latter. The earthy matter is composed chiefly 
o^ lihosphate of lime, but besides there is a small quantity, 
about 1 1 of the 6"/ per cent., of carbonate of lime, with 
minute quantities of some other salts. The animal matter 
is resolved into gelatine by boiling. The earthy and 
animal constituents of bone are so intimately blended and 
incorporated the one with the other, that it is only by 
chemical action, as for instance, by heat in one case, and 
by the action of acids in another, that they can be sepa- 
rated. Their close union, too, is further shown by the 
fact that when by acids the earthy matter is dissolved out, 
or, on other band, when the animal part is burnt out, 
the general shape of the bone is alike preserved. 

To the naked eye there appear two kinds of structure 
in different bones, and in different parts of the same bone, 
namely, the dense or compact, and the cancellous tissue. 
Thus, in making a longitudinal section of a long bone, as 
the humerus or femur, the articular extremities are found 
capped on their surface by a thin shell of comjmct bone, 
while their interior is made up of the spongy or cancellous 
tissue. The shaft, on the other hand, is formed almost 
entirely of a thick layer of the comvact bone, and this sur- 
rounds a central canal, the medullary cavity — so called from 
its containing the medulla or marrow (p. 39). In the flat 
bones, as the parietal bone or the scapula, one layer of 
the cancellous structure lies between two layers of the 
compact tissue, and in the short and irregular bones, as 
those of the carpus and tarsus, the cancellous tissue alone 



46 



ELEMENTARY TISSrES. 



fills the interior, while a thin shell of compact bone forms 
the outside. The spaces in the cancellous tissue are filled 
by a species of marrow, which differs considerably from 
that of the shaft of the long bones. It is more fluid, and 
of a reddish colour, and contains very few fat cells. 

The surfaces of bones, except the parts covered with 
articular cartilage, are clothed by a tough fibrous mem- 
brane, the jjeriosteum ; and it is from the blood-vessels 
which are distributed first in this membrane, that the 
Fkj. 1 6.* 




bones, especially their more compact tissue, are in great 
part supplied with nourishment, — minute branches from 
the periosteal vessels entering the little foramina on the 
surface of the bone, and finding their way to the Haversian 
canals, to be immediately described. The long bones are 

* Fig. 1 6. Transverse section of compact tissue (of humerus) mag- 
nified abput 150 diameters. Three of the Haversian canals are seen, 
•with their concentric rings ; also the corpuscles or lacunae, with the 
canaliculi extending from them across the direction of the lamellre. The 
Haversian apertures had got filled with debris in grinding down the 
section, and therefore appear black in the figure, Avhich represents the 
object as viewed with transmitted light (after Sharpey). 



EOXE. 



47 



supplied also by a proper nutrient artery, which entering 
at some part of the shaft so as to reach the medullary 
canal, breaks up into branches for the supply of the marrow, 
from which again small vessels are distributed to the inte- 
rior of the bone. Other small blood-vessels pierce the arti- 
cular extremities for the supply of the cancellous tissue. 

Notwithstanding the differences of arrangement just 
mentioned, the structure of all bone is found, under the 
microscope, to be essentially the same. Examined with a 
rather high power, its substance is found occupied by a 
multitude of little spaces, called lacunce, with very minute 
canals or canalicidi, as they are termed, leading from them, 
and anastomosing with similar little prolongations from 
other lacunte (fig. i6). In very thin layers of bone, no 
other canals than these may be 
visible; but on making a transverse 
section of the compact tissue, e.g., 
of a long bone, as the humerus or 
ulna, the arrangement shewn in 
fig. 1 6 can be seen. The bone seems 
mapped out into small circular dis- 
tricts, at or about the centre of each 
of which is a hole, and around this 
an appearance as of concentric 
layers — the lacwicB and canalicidi fol- 
lowing the same concentric plan of 
distribution around the small hole 
in the centre, with which, indeed, 
they communicate. On making a 
longitudinal section, the central 
holes are found to be simply the cut extremities of small 
canals which run lengthwise through the bone (fig. 1 7), and 




* Fig. 17. Haversian canals, seen in a longitudinal section of the 
compact tissue of tlie shaft of one of the long bones, a. Arterial canal ; 
h. Venous canal ; c. Dilatation of another venous canal. 



48 ELEMEXTARY TISSUES. 

are called Haversian canals, after the name of the physician, 
Clopton Havers, who first accurately described them. 

The Haversian canals, the average diameter of which 
is 3-1-^ of an inch, contain blood-vessels, and by means of 
them, blood is conveyed to all, even the densest parts 
of the bone ; the minute canaliculi and lacuna? abs^bing 
nutrient matter from the Haversian blood-vessels, and con- 
veying it still more intimately to the very substance of the 
bone which they traverse. The blood-vessels enter the 
Haversian canals both from without, by traversing the 
small holes which exist on the surface of all bones beneath 
the periosteum, and from within by means of small channels, 
which extend from the medullary cavity, or from the can- 
cellous tissue. According to Todd and Bowman, the arteries 
and veins usually occupy separate canals, and the veins 
which are the larger, often present, at irregular intervals, 
small pouch-like dilatations (fig. 17). 

The lacuna are occupied by nucleated cells, or, as Dr. 
Beale expresses it, minute portions of protoplasm or 
germinal matter ; and there is every reason to believe that 
the lacunar cells are homologous with the corpuscles of 
the connective tissue, each little particle of protoplasm 
ministering to the nutrition of the bone immediately 
surrounding it, and one lacunar particle communicating 
with another, and with its surrounding district, and with 
the blood-vessels of the Haversian canals, by means of 
the minute streams of fluid nutrient matter which occupy 
the canaliculi. 

Besides the concentric lamellcB of bone tissue which 
surround the Haversian canal in the shaft of a long bone, 
are others, especially near the circumference, which 
surround the whole bone, and are arranged concentrically 
with regard to the medullary canal. 

The ultimate structure of the lamellcB appears to be 
reticular. If a thin film be peeled off the surface of a bone 
from which the earthy matter has been removed by acid, 



BOXE. 



49 




and examined with a high power of the microscope, it will 
be found composed, according to Sharpey, of a finely 
reticular structure, formed appa- 
rently of very slender fibres decus- 
sating obliquely, but coalescing at 
the points of intersection, as if here 
the fibres were fused rather than 
woven together (fig. i8). 

In many places these reticular 
lamellse are perforated by tapering 
fibres, resembling in character the 
ordinary white or rarely the elastic 
fibrous tissue, which bolt the neigh- 
bouring lamella) together, and may 
be drawn out when the latter are torn asunder (fig. 19). 

Bone is developed after two different fashions. In one, 
the tissue in which the earthy matter is laid down is a 
membrane, composed mainly of fibres and granular cells, 
like imperfectly developed connective-tissues. Of this kind 
of ossification in membrane, the flat bones of the skull 
are examples, in the other, and much more common case, 
of which a long bone may be cited as an instance, the 
ossification takes place in cartilage. 

In most bones ossification begins at more than one 
point; and from these centres of ossification, as they are 
called, the process of deposition of calcareous matter 
advances in all directions. Bones grow by constant de- 
velopment of the cartilage or membrane between these 
centres of ossification, until by the process of calcification 
advancing at a quicker rate than the development of the 
softer structures, the bone becomes impregnated through- 



* Fig. 18. Thin layer peeled off from a softened bone, as it appears 
under a magnifying power of 400. — Tliis figure, which is intended to 
represent the reticular structure of a lamella, gives a better idea of the 
object when held rather farther off than usual from the eye (from 
Sharpey). 



50 



ELEMEI^TTARY TISSUES. 



out with, calcareous matter, and can grow no more. In 
the long bones the main centres of ossification are seated 
at the middle of the shaft, and at each of tlie extremities. 
Increase of the length of bones, therefore, occurs at the part 
which intervenes between the ossifying centre in the shaft 




"'^ 



^^ 



V. ;v y^^'^'^^ 



•^ ^^•^::'^c^^^^5s -^-x 



and that at each extremity ; while increase in thickness takes 
place by the formation of layers of osseous tissue beneath 
the periosteum. The former is an example of ossification 
in cartilage ; the latter of ossification in membrane. 

Teeth. — A tooth is generally described as possessing a 
crown, neck, and fang, or fangs. The crown is the portion 
which projects beyond the level of the gum. The nech is 
that constricted portion just below the crown which is 



* Fig. 19. Lamellae torn off from a decalcified human parietal bone 
at some depth from the surface, a, a lamella, sho"\\-ing reticular fibres ; 
h, b, darker part, where several lamellaj are superposed ; c, c, perforating 
fibres. Apertures through which perforating fibres had passed, are seen 
especially in the lower part, a, a, of the figure. Magnitude as seen 
under a power of 200, but not drawn to a scale (from a drawing by 
Dr. Allen Thomson). 



TEETH. 



51 




embraced by the free edges of the gum, and the fang 
includes all below this. 

On making a longitudinal section through the centre 
of a tooth (figs, 20 and 21), 

it is found to be princi- Fig. 20.* 

pally composed of a hard 
matter, dentine or ivory ; 
while in the centre this 
dentine is hollowed out 
into a cavity resembling in 
general shape the outline 
of the tooth, and called the 
pulp -cavity J from its containing a very vascular and sensi- 
tive little mass composed of connective tissue, blood-vessels 
and nerves, which is called the tooth-pulp. The pulp is 
continuous below, through an opening at the end of the 
fang, with the mucous membrane of the gum. Capping 
that part of the dentine which projects beyond the level 
of the gum, is a layer of very hard calcareous matter, the 
enamel, while sheathing the portion of dentine which is 
beneath the level of the gum, is a layer of true bone, called 
the cement or crusta petrosa. At the neck of the tooth the 
cement is exceedingly thin, but it gradually becomes thicker 
as it approaches and covers the lower end or apex of the 
fang. 

Dentine or ivory in chemical composition closely re- 
sembles bone. It contains, however, rather less animal 
matter; the proportion in lOO parts being about 28 of animal 
matter to 72 of earthy. The former, like the animal matter 
of bone, may be resolved into gelatin by boiling. The 



* Fig. 20. Sections of an Incisor and Molar Tooth. — The longitudinal 
sections show the whole of the pulp-cavity in the incisor and molar 
teeth, its extension upwards within the crown, and its prolongation 
downwards into the fangs, with the small aperture at the point of each : 
these and the cross section show the relation of the dentine and enamel. 

E 2 



52 



ELEMENTAEY TISSUES. 



Fig. 21.* 



earthy matter is made up chiefly of phosphate of lime, 
with a small portion of the carbonate, and traces of some 
other salts. 

Under the microscope, dentine is 
seen to be finely channelled by a mul- 
titude of fine tubes, which, by their 
inner ends, communicate with the 
pulp-cavity, and by their outer extre- 
mities come into contact with the 
under part of the enamel and cement, 
and sometimes even penetrate themi 
for a greater or less distance. In 
their course from the pulp- cavity to 
the surface of the dentine, these mi- 
nute tubes form gentle and nearly 
parallel curves, and divide and sub- 
divide dichotomously, but without 
much lessening of their calibre until 
they are approaching their peripheral 
termination. From their sides proceed 
other exceedingly minute secondary 
canals, which extend into the dentine 
between the tubules. 

The tubules of the dentine, the 
average diameter of which at their 
inner and larger extremity is 43^770- ^^ ^^ inch, contain fine 
prolongations from the tooth-pulp which give the dentine 
a certain faint sensitiveness under ordinary circumstances, 
and, without doubt, have to do also with its nutrition. 




* Fig. 21. Magnified Longitudinal Section of a Bicuspid Tooth 
(after Eetzius) — i, the ivory or dentine, showing the direction and 
primary curves of the dental tuhuli ; 2, the pulp-cavity, with the 
small apertures of the tubuli into it ; 3, the cement or crusta petrosa, 
covering the fang as high as the border of the enamel at the neck, 
exhibiting lacunae ; 4, the enamel resting on the dentine ; this has been 
worn away by use from the upper part. 



TEETH. 



53 



Fig. 22.* 



The enamel, wMcli is by far the hardest portion of a 
tooth, is composed, chemically, of the same elements that 
■enter into the composition of dentine and bone. Its 
animal matter, however, amounts only to about 2 or 3 per 
<}ent. 

Examined under the microscope, 
■enamel is found composed of fine 
hexagonal fibres (figs. 22 and 23), 
which are set on end on the sur- 
face of the dentine, and fit into 
corresponding depressions in the 
same. They radiate in such a 
manner from the dentine, that at 
the top of the tooth they are more 
or less vertical, while towards the 
sides they tend to the horizontal 
direction. Like the dentine-tu- 
bules, they are not straight, but 
disposed in wavy and parallel 
curves. The fibres are marked by 
transverse lines, and are mostly 
solid, but some of them contain a 
very minute canal. 

The enamel itself is coated on 
the outside by a very thin calcified 
membrane, sometimes termed the 
cuticle of the enamel. 

The crusta jpetrosa, or cement, is composed of true bone, 
and in it are lacunse and canaliculi which sometimes 
communicate with the outer finely-branched ends of the 
dentine- tubules . 




* Fig, 22. Thin section of the enamel and a part of the dentine 
<from Kolliker) ^. «, cuticular pellicle of the enamel ; &, enamel 
fibres, or columns with fissures between them and cross strise ; c, larger 
cavities in the enamel, commimicatiug with the extremities of some of 
the tubuli (d). 



54 



ELEMENTARY TISSUES. 



Development of Teeth. — The teeth are developed after the 
following manner : — Along the free edge of the tooth- 
less gum in the foetus, there extends a groove, or small 

Fig. 23.* 




trench, the primitive dental groove (Goodsir), and, from the 
bottom of this, project ten small processes of mucous mem- 
brane, or papillce, containing blood-vessels and nerves. As 
these papillce grow up from below, the edges of the small 
trench begin to grow in towards each other, and over- 
shadow them, at the same time that each papilla is cut off 
from its neighbour by the extension of a partition wall 
from the gum, which grows in from each side to separate 
the one from the other. Thus closed in above and all 
around, each dental papilla is at length contained in a 
separate sac, and gradually assumes the character of a 
tooth by deposition on its surface of the various hard 
matters which have been just enumerated as composing 
the greater part of a tooth's substance. The small vascular 

* Fipf. 23. Enamel fibres { from KoUiker) 4"°« -^f fragments and 
single fibres of the enamel, isolated by the action of hydrochloric acid. 
B, surface of a small fragment of enamel, showing the hexagonal ends 
of the fibres. 



DEVELOPMEXT OF TEETH. 55 

papilla is gradually encroached upon and imprisoned by 
the calcareous deposit, until only a small part of it is left 
as the tooth-pulp, which remains shut up in the harder 
substance, with only the before-mentioned small communi- 
cation with the outside, through the end of the fang. In 
this manner the first set of teeth, . or the milk-teeth, are 
formed; and each tooth, by degrees developing, presses 
at length on the wall of the sac enclosing it, and causing 
its absorption, is cut, to use a familiar phrase. 

The temporary or milk-teeth, having only a very limited 
term of existence, gradually decay and are shed, while 
the permanent teeth push their way from beneath, by 
gradual increase and development, so as to succeed them. 

The temporary teeth are ten in each jaw, namely, four 
incisors, two canines, and four molars, and are replaced by ten 
permanent teeth, each of which is developed from a small 
sac set by, so to speak, from the sac of the temporary tooth 
which precedes it, and called the cavity of reserve. The 
number of the permanent teeth is, however, increased to 
sixteen, by the development of three others on each side of 
the jaw after much the same fashion as that by which the 
milk teeth were themselves formed. The beginning of 
the development of the permanent teeth of course takes 
place long before the cutting of those which they are to 
succeed ; one of the first acts of the newly-formed little 
dental sac of a milk-tooth being to set aside a portion of 
itself as the germ of its successor. 

The following formula shows, at a glance, the com- 
parative arrangement and number of the temporary and 
permanent teeth : — 

MO. CA. IX. CA, MO. 

( Upper 2 I 4 I 2 =10 

Temporary Teeth . < = 20 

( Lower 2 i 4 i 2 =10 

MO.BI. CA. IX. CA. BI. MO. 

(Upper 32 141 23= 16 

Permanent Teeth. < =32 

(Lower 3 2 i 4 i 2 3=16 



56 THE BLOOD. 

From this formula it will be seen that the two bicuspid 
teeth in the adult are the successors of the two molars in 
the child. They differ from them, however, in some 
respects, the temporary molars having a stronger likeness 
to the permanent than to their immediate descendants, the 
so-called bicuspids. The temporary incisors and canines 
differ but little, except in their smaller size, from their 
successors. 



CHAPTER V. 

THE BLOOD. 

Although it may seem, in some respects, unadvisable to 
describe the blood before entering upon the physiology of 
those subservient processes which have for their end or 
purpose its formation and development, yet there are 
many reasons for taking such a course, and we may there- 
fore at once proceed to consider the structural and chemical 
composition of this fluid. 

Wherever blood can be seen under a moderately high 
microscope-power as it flows in the vessels of a living part, 
it appears a colourless fluid containing minute coloured 
particles. The greater part of these particles are red, when 
seen en masse, and they are the source of the colour which, 
so far as the naked eye can see, belongs to every part of the 
blood alike. The colourless fluid is named liquor sanguinis ; 
the particles are the hloocl corpuscles or hlood-cells. The struc- 
tural composition of the blood may be thus expressed : — 

(corpuscles ) ^^""^ (containing also 

T • -J T>i J ) i inoi'G or less serum). 

Liqmd Blood j liquor Sanguinis j Fibrin ) 

( or Plasma. ( Serum 

When blood flows from the living body, it is a thickish 
heavy fluid, of a bright scarlet colour when it comes from 
an artery ; deep purple, or nearly black, when it flows from 



ODOUR OF BLOOD. 57 

a vein. Its specific gravity at 60° F. is, on an average, 
1055, that of water being reckoned as lOOO; the extremes 
consistent with health being 1050 and 1059. ^^^ tempera- 
ture is generally about ioo° F. ; but it is not the same in 
all parts of the body. Thus, while the stream is slight^ 
warmed by passing through the liver and some other parts, 
it is slightly cooled, according to Bernard, by traversing 
the capillaries of the skin. The temperature of blood in 
the left side of the heart is, again 1° or 2° higher than in 
the right (Savory). 

The blood has a slight alkaline reaction ; and emits an 
odour similar to that which issues from the skin or breath 
of the animal from which it flows, but fainter. The alka- 
line reaction appears to be a constant character of blood 
in all animals and under all circumstances. An exception 
has been supposed to exist in the case of menstrual blood; 
but the acid reaction which this sometimes presents is due 
to the mixture of an acid mucus from the uterus and 
vagina. Pure menstrual blood, such as may be obtained 
with a speculum, or from the uteri of women who die 
during menstruation, is always alkaline, and resembles 
ordinary blood. According to Bernard, blood becomes 
spontaneously acid after removal from the body, owing to 
conversion of its sugar into lactic acid. 

The odour of blood is easily perceived in the watery 
vapour, or halitus as it is called, which rises from blood 
just drawn : it may also be set free, long afterwards, by 
adding to the blood a mixture of equal parts of sulphuric 
acid and water. It is said to be not difficult to tell, by the 
likeness of the odour to that of the body, the species of 
domestic animal from which any specimen of blood has 
been taken : the strong odour of the pig or cat, and the 
peculiar milky smell of the cow, are especially easy to be 
thus discerned in their blood (Barruel). 



58 THE BLOOD. 

Quantity/ of Blood. 

Only an imperfect indication of the whole quantity of 
blood in the body is afforded by measurement of that 
which escapes, when an animal is rapidly bled to death, 
inasmuch as a certain amount always remains in the blood- 
vessels. In cases of less rapid bleeding, on the other 
hand, when life is more prolonged, and when, therefore, 
sufficient time elapses before death to allow some absorp- 
tion into the circulating current of the fluids of the body 
(p. 84), the whole quantity of blood that escapes may be 
greater than the whole average amount naturally present 
in the vessels. 

Various means have been devised, therefore, for obtain- 
ing a more accurate estimate than that which results from 
merely bleeding animals to death. 

"VVelcker's method is the following. An animal is 
rapidly bled to death, and the blood which escapes is col- 
lected and measured. The blood remaining in the smaller 
vessels is then removed by the injection of water through 
them, and the mixture of blood and water thus obtained, 
is also collected. The animal is then finely minced, and 
infused in water, and the infusion is mixed with the com- 
bined blood and water previously obtained. Some of this 
fluid is then brushed on a white ground, and the colour 
compared with that of mixtures of blood and water whose 
proportions have been previously determined by measure- 
ment. In this way the materials are obtained for a fairly 
exact estimate of the quantity of blood actually existing in 
the body of the animal experimented on.' 

Another method (that of Vierordt) consists in estimating 
the amount of blood expelled from the ventricle, at each 
beat of the heart, and multiplying this quantity by the 
number of beats necessary for completing the 'round' of 
the circulation. This method is ingenious, but open to 
various objections, the most conclusive being the uncer- 



QUANTITY OF BLOOD. 59 

tainty of all the premisses on whicli the conclusion is 
founded. 

Other methods depend on the results of injecting a 
known quantity of water (Valentin) or of saline matters 
(Blake) into the blood-vessels; the calculation being 
founded in the first case, on the diminution of the specific 
gravity which ensues, and in the other, on the quantity of 
the salt found diffused in a certain measured amount of 
the blood abstracted for experiment. 

A nearly correct estimate was probably made by Weber 
and Lehmann, from the following data. A criminal was 
weighed before and after decapitation; the difference in 
the weight representing, of course, the quantity of blood 
which escaped. The blood-vessels of the head and trunk, 
were then washed out by the injection of water, until the 
fluid which escaped had only a pale red or straw colour. 
This fluid was then also weighed ; and the amount of blood 
which it represented was calculated, by comparing the 
proportion of solid matter contained in it, with that of the 
first blood which escaped on decapitation. Two experi- 
ments of this kind gave precisely similar results. 

The most reliable of these various means for estimating 
the quantity of blood in the body yield as nearly similar 
results as can be expected, when the sources of error un- 
avoidably present in all, are taken into consideration; and 
it may be stated that in man, the weight of the whole 
quantity of blood, compared with that of the body, is from 
about I to 8, to I to 10. 

It must be remembered, however, that the whole quan- 
tity of blood varies, even in the same animal, very consider- 
ably, in correspondence with the different amounts of food 
and drink, which may have been recently taken in, and 
the equally varying quantity of matter given out. Bernard 
found by experiment, that the quantity of blood obtainable 
from a fasting animal is scarcely more than a half of that 
which is present soon after a full meal. The estimate above 



6o THE BLOOD 

given, must therefore be taken to represent only an ap- 
proximate average. 



Coagulation of the Blood. 

When blood is drawn from the body, and left at rest, 
certain changes ensue, which constitute a kind of rough 
analysis of it, and are instructive respecting the nature of 
some of its constituents. After about ten minutes, taking 
a general average of many observations, it gradually clots 
or coagulates, becoming solid like a soft jelly. The clot 
thus formed has at first the same volume and appearance 
as the fluid blood had, and, like it, looks quite uniform ; 
the only change seems to be, that the blood which was fluid 
is now solid. But presently, drops of transparent yellowish 
fluid begin to ooze from the surface of the solid clot ; and 
these gradually collecting, first on its upper surface, and 
then all around it, the clot or " crassamentum,^^ diminished 
in size, but firmer than it was before, floats in a quantity 
of yellowish fluid, which is named serum, the quantity of 
which may continually increase for from twenty -four to 
forty-eight hours after the clotting of the blood. 

The changes just described maybe thus explained. The 
liquor sanguinis, or liquid part of the blood (p. 56), consists 
of a thin fluid called serum, holding fibrin in solution.*^- 
The peculiar property of fibrin, as already said, is its ten- 
dency to become solid when at rest, and in some other 
conditions. When, therefore, a quantity of blood is drawn 
from the vessels, the fibrin coagulates, and the blood cor- 
puscles, with part of the serum, are held, or, as it were, 
entangled in the solid substance which it forms. 

But after healthy fibrin has thus coagulated, it always 



* This statement has been left nnaltered in the text ; but, as will be 
seen farther on, it recjuires modification. — (Ei>.) 



COAGULATIOX OF BLOOD. ' 6 1 

contracts ; and what is generally described as one process 
of coagulation should rather be regarded as consisting of 
two parts or stages ; namely, first, the simple act of clot- 
ting, coagulating, or becoming solid; and, secondly, the 
contraction or condensation of the solid clot thus formed. 
By this second act much of the serum which was soaked 
in the clot is gradually pressed out ; and this collects in 
the vessel around the contracted clot. 

Thus, by the observation of blood within the vessels, and 
of the changes which commonly ensue when it is drawn 
from them, we may distinguish in it three principal consti- 
tuents, namely, 1st, the fibrin, or coagulating substance > 
27id, the serum ; yd, the corpuscles. 

That the fibrin is the only spontaneously coagulable 
material in the blood, may be proved in many ways ; and 
most simply by employing any means whereby a portion 
of the liquor sanguinis, i.e., the serum and fibrin, can be- 
separated from the red corpuscles before coagulation. 
Under ordinary circumstances coagulation occurs before^ 
the red corpuscles have had time to subside ; and thus, 
from their being entangled in the meshes of the fibrin, the 
clot is of a deep dark red colour throughout, — somewhat 
darker, it may be, at the most dependent part, from accu- 
mulation of red cells, but not to any very marked degree. 
If, however, from any cause, the red cells sink more 
quickly than usual, or the fibrin contracts more slowly, 
then, in either of these cases, the red corpuscles may be 
observed, while the blood is yet fluid, to sink below its 
surface ; and the layer beneath which they have sunk, and 
which has usually an opaline or greyish white tint, will 
coagulate without them, and form a white clot consisting 
of fibrin alone, or of fibrin with entangled white cor- 
puscles ; for the white corpuscles, being very light, tend 
upwards towards the surface of the fluid. The layer of 
white clot which is thus formed rests on the top of a 
coloured clot of ordinary character, i.e., of one in which 



62 THE BLOOD. 

the coagulating fibrin has entangled the red corpuscles 
while they were sinking : and, thus placed, it constitutes 
what has been called a huffy coat. 

When a buffy coat is formed in the manner just de- 
scribed, it commonly contracts more than the rest of the 
clot does, and, drawing in at its sides, produces a cupped 
appearance on the top of the clot. 

In certain conditions of the system, and especially when 
there exists some local inflammation, this buffed and 
cupped condition of the clot is well marked, and there has 
been much discussion concerning its origin under these 
circumstances. It is now generally agreed that two causes 
combine to produce it. 

In the first place, the tendency of the red corpuscles to 
form rouleaux (see p. 73) is much exaggerated in inflam- 
matory blood : and as their rate of sinking increases with 
their aggregation, there is a ready explanation, at least in 
part, of the colourless condition of the top of the clot. 
And in the next place, inflammatory blood coagulates less 
rapidly than usual, and thus there is more time for the 
already rapidly sinking corpuscles to subside. The colour- 
less or buffed condition of the upper part of the clot is there- 
fore, readily accounted far ; while the cupped appearance is 
easily explained by the greater power of contraction pos- 
sessed by the fibrin of inflammatory blood, and by its 
contraction being now not interfered with by the presence 
of red corpuscles in its meshes. 

Although the appearance just described is commonly 
the result of a condition of the blood in which there is an 
increase in the quantity of fibrin, it need not of necessity 
be so. For a very different state of the blood, such as 
that which exists in chlorosis, may give rise to the same 
appearance ; but in this case the pale layer is due to a 
relatively smaller amount of red corpuscles, not to any 
increase in the quantity of fibrin. 

It is thus evident that the coagulation of the blood is due 



COAGULATION OF BLOOD. 63 

to its fibrin. The cause of tlie coagulation of the fibrin, 
however, is still a mystery. 

The theory of Prof, Lister, that fibrin has no natural 
tendency to clot, but that its coagulation out of the body 
is due to the action of foreign matter with which it 
happens to be brought into contact, and, in the body, 
to conditions of the tissues, which cause them to act 
towards it like foreign matter, is insufficient ; because 
even if it be true, it still leaves unexplained the manner 
in which the fibrin, fluid in the living blood-vessels, can, 
by foreign matter, be thus made solid. If it be 
a fact, it is a very important one, but it is not an 
explanation. 

The same remark may be applied also to another theory 
which differs from the last, in that while it admits a 
natural tendency on the part of the blood to coagulation, 
it supposes that this tendency in the living body is re- 
strained by some inhibitory power resident in the walls of 
the containing vessels. This also may, or may not, be 
true; but it is only a statement of a possible fact, and 
leaves unexplained the manner in which living tissue can 
thus restrain coagulation. 

Dr. Draper believes that coagulation takes place in the 
living body, as out of it, or as in the dead ; but in the one 
case the fibrin is picked out in the course of the circu- 
lation by tissues which this particular constituent of 
the blood is destined to nourish ; in the others, it remains 
and becomes evident as a clot. This explanation is inge- 
nious, but requires some kind of proof before it can be 
adopted. 

Concerning other theories, as for instance, that coagu- 
lation is due to the escape of carbonic acid, or of ammonia, 
it need only be said that they have been completely 
disproved. 

We must, therefore, for the present, believe that the 
cause of the coagulation of the blood has yet to be dis- 



64 THE BLOOD. 

covered; but some very interesting observations in con- 
nexion with the subject have been recently made, and seem 
not unlikely to lead in time to a solution of this difficulfc 
and most vexed question. The observations referred to 
have been made independently by Alexander Schmidt, 
although he was forestalled in regard to some of his ex- 
periments by Dr. Andrew Buchanan of Glasgow, many 
years ago. 

When blood-serum, or washed blood-clot, is added to 
the fluid of hydrocele, or any other serous effusion, it 
speedily causes coagulation, and the production of true 
fibrin. And this phenomenon occurs also on the ad- 
mixture of serous effusions from different parts of the 
body, as that of hydrocele with that of ascites, or of either 
with fluid from the cavitj^ of the pleura. Other sub- 
stances also, as muscular or nervous tissue, skin, etc., 
have been found also able to excite coagulation in serous 
fluids. Thus, fluids which have little or no tendency to 
coagulate when left to themselves, can be made to produce 
a clot, apparently identical with the fibrin of blood by 
the addition to them of matter which, on its part, was not 
known to have any special relation to fibrin. As may be 
supposed, the coagulation is not alike in extent under all 
these circumstances. Thus, although it occurs when ap- 
parently few or no blood-ceUs exist in either constituent of 
the mixture, yet the addition of these very much increases 
the effect, and their presence evidently has a very close 
connexion with the process. From the action of the buffy 
coat of a clot, in causing the appearance of fibrin in serous 
effusions, it may be inferred that the pale as well as the 
red corpuscles are influential in coagulation under these 
circumstances. Blood-crystals are also foun^ to be effec- 
tive in producing a clot in serous fluids. 

The true explanation of these very curious phenomena 
is, probably, not fully known ; but Schmidt supposes that 
in the act of formation of fibrin there occurs the union 



FOEMATIOX OF FIBRIK 65 

of two substances, which, he terms fibrino-plastin and 
fibrinogen. 

The substance which he terms fibrino-plastin, and which 
he has obtained, not only from blood, but from many 
other liquids and solids, as the crystalline lens, chyle and 
lymph, connective tissue, etc., which are found capable of 
exciting coagulation in serous fluids, is probably identical 
with the globulin of the red corpuscles. , 

The fibrinogenous matter obtained from serous effusions 
differs but little, chemically, from the fibrino-plastin. 

Thus in the experiment before mentioned, the globulin 
or fibrino-plastic matter of the blood-cells, in the clot, 
causes coagulation by uniting with the fibrinogen present 
in the hydrocele-fluid. And whenever there occurs coagu- 
lation with the production of fibrin, whether in ordinary 
blood-clotting, or in the admixture of serous effusions, or 
in any other way, a like union of these two substances may 
be supposed to occur. 

The main result, therefore, of these very interesting 
experiments and observations has been to make it probable 
that the idea of fibrin existing in a liquid state in the 
blood is founded on a mistaken notion of its real nature, 
and that, probably, it does not exist at all in solution as 
fibrin, but is formed at the moment of coagulation by 
the union of two substances which, in fluid blood, exist 
separately. 

The theories before referred to, concerning the coagu- 
lation of the blood, will therefore, if this be true, resolve 
themselves into theories concerning the causes of the union 
of fibrino-plastin and fibrinogen ; and whether, on the one 
hand, it is an inhibitory action of the living blood-vessels 
that naturally restrains, or a catalytic action of foreign 
matter that excites, the union of these two substances. 



66 THE BLOOD. 

Conditions affecting Coagulation. 

Although the coagulation of fibrin appears to be spon- 
taneous, yet it is liable to be modified by the conditions in 
which it is placed ; such as temperature, motion, the access 
of air, the substances with which it is in contact, the mode 
of death, etc. All these conditions need to be considered 
in the study of the coagulation of the blood. 

The coagulation of the blood is hastened by the follow- 
ing means : — 

1. Moderate warmth, — from about ioo° F. to I20° F. 

2. Hest is favourable to the coagulation of blood. Blood, 
of which the whole mass is kept in uniform motion, as 
when a closed vessel completely fiUed with it is constantly 
moved, coagulates very slowly and imperfectly. But rest 
is not essential to coagulation ; for the coagulated fibrin 
may be quickly obtained from blood by stirring it with 
a bundle of small twigs ; and whenever any rough points 
of earthy matter or foreign bodies are introduced into 
the blood-vessels, the blood soon coagulates upon them. 

3. Contact with foreign matter, and especially multi- 
plication of the points of contact. Thus, when all other 
conditions are unfavourable, the blood wiU coagulate upon 
rough bodies projecting into the vessels ; as, for example, 
upon threads passed through arteries or aneurismal sacs, 
or the heart's valves roughened by inflammatory deposits 
or calcareous accumulations. And, perhaps, this may 
explain the quicker coagulation of blood after death in the 
heart with walls made irregular by the fleshy columns, 
than in the simple smooth-walled arteries and veins. 

4. The free access of air. 

5. Coagulation is quicker in shallow, than in tall and 
narrow vessels. 

6. The addition of less than twice the bulk of water. 
The blood last drawn is said to coagulate more quickly 

than that which is first let out. 



COXDITIOXS AFFECTING COAGULATIOX. 6/ 

The coagulation of the blood is retarded by the following 
means : — 

1 . Cold retards the coagulation of blood ; and it is said 
that, so long as blood is kept at a temperature below 40° 
F., it will not coagulate at all. Freezing the blood, of 
course, prevents its coagulation; yet it will coagulate, 
though not firmly, if thawed after being frozen ; and it 
will do so, even after it has been fi ozen for several months. 
Coagulation is accelerated, but the subsequent contraction 
of the clot is hindered, by a temperature between I00° and 
120° : a higher temperature retards coagulation, or, by 
coagulating the albumen of the serum, prevents it 
altogether. 

2. The addition of water in greater proportion than 
twice the bulk of the blood. 

3. Contact with living tissues, and especially with the 
interior of a living blood-vessel, retards coagulation, 
although if the blood be at rest it does not prevent it, 

4. The addition of the alkaline and earthy salts in the 
proportion of 2 or 3 per cent, and upwards. When added 
in large proportion most of these saline substances pre- 
vent coagulation altogether. Coagulation, however, en- 
sues on dilution with water. The time that blood can be 
thus preserved in a liquid state and coagulated by the 
addition of water, is quite indefinite. 

5 . Imperfect aeration, — as in the blood of those who die 
by asphyxia. 

6. In Inflammatory states of the system, the blood coa- 
gulates more slowly although more firmly. 

7. Coagulation is retarded by exclusion of the blood 
from the air, as by pouring oil on the surface, etc. In 
vacuo, the blood coagulates quickly ; but Prof. Lister 
thinks that the rapidity of the process is due to the bub- 
bling which ensues from the escape of gas, and to the 
blood being thus brought more freely into contact with the 
containing vessel. 

F 2 



6S THE BLOOD. 

The coagulation of the blood is prevented altogether by 
the addition of strong acids and caustic alkalies. 

It has been believed, and chiefly on the authority of Mr. 
Hunter, that, after certain modes of death, the blood does 
not coagulate; he enumerates the death by lightning, 
over-exertion (as in animals hunted to death), blows on the 
stomach, fits of anger. He says, *' I have seen instances 
of them all." Doubtless he had done so ; but the results 
of such events are not constant. The blood has been often 
observed coagulated in the bodies of animals killed by 
lightning or an electric shock ; and Mr. Gulliver has 
published instances in which he found clots in the hearts 
of hares and stags hunted to death, and of cocks killed in 
fighting. 

Chemical Composition of the Blood. 

Among the many analyses of the blood that have been 
published, some, in which all the constituents are enume- 
rated, are inaccurate in their statements of the proportions 
of those constituents ; others, admirably accurate in some 
particulars, are incomplete. The two following Tables, 
constructed chiefly from the analyses of Denis, Lecanu, 
Simon, Nasse, Lehmann, Becquerel, Rodier, and Gavarret, 
are designed to combine, as far as possible, the advan- 
tage of accuracy in numbers with the convenience of 
presenting at one view, a list of all the constituents of the 
blood. 

Average proportions of the principal constituents of the 
blood in i,ooo parts : — 

Water 784- 

Eed corpuscles (solid residue) 130" 

Albumen of serum 70* 

Saline matters . . . . . . . . 6 "03 

Extractive, fatty, and other matters . . . 777 
Fibrin 2*2 



ICOO" 



COMPOSITION OF BLOOD. 69 

Average proportions of all the constituents of tb.e blood 
in 1,000 parts: — 

Water 784' 

Albumen. ........ 70* 

Fibrin 2*2 

Eed coqmscles (dry) . . . . . . i30- 

' Fatty matters . . . . . . . . i '4 

Inorganic salts : Cliloride of sodium . . . 3*6 

Chloride of potassium . . . 0*35 

Tribasic phospliate of soda . . o'2 

Carbonate of soda . . . . 0'2S 

Sulphate of soda . . . . o'28 

Phosphates of lime and magnesia . 0*25 

Oxide and phosphate of iron . 0*5 

Extractive matters, biliary colouring matter, gases, 

and accidental substances . . . . 6-40 

1000 • 
Elementary composition of the dried blood of the ox : — 

Carbon 57 '9 

Hydrogen 7*i 

Nitrogen . . • . . . . . I7'4 

Oxygen ......... 19*2 

Ashes 4"4 

These results of the ultimate analysis of ox's blood afford 
a remarkable illustration of its general purpose, as supply- 
ing the materials for the renovation of all the tissues. For 
the analysts (Play fair and Boeckmann) have found that 
the flesh of the ox yields the same elements in so nearly 
the same proportions, that the elementary composition of 
the organic constituents of the blood and flesh may be con- 
sidered identical, and may be represented for both by the 
formula C^^HggNeOij. 

Tlie Blood' Corpuscles or Blood-Cells.] 

It has been already said, that the clot of blood contains, 
with the fibrin and the portion of the serum that is soaked 
in it, the hlood-corpuscles, or blood-cells. Of these there are 



70 



THE ELOOD. 



two principal forms, the red and the white corpuscles. 
When coagulation has taken place quickly, both kinds of 

Fig. 24.* 
Mammals. Birds. Reptiles. Amphibia. Fish. 




* The above illustration is somewhat altered from a drawing, by Mr. 
Gulliver, in the Proced. Zool. Society, and exhibits the typical characters 
of the red-blood cells in the main divisions of the Vertebrata. The 
fractions are those of an inch, and represent the average diameter. In 



RED BLOOD-CORPUSCLES. 



71 



corpuscles may be uniformly diffused through the clot ; 
but, when it has been slow, the red corpuscles, being the 
heaviest constituent of the blood, tend by gravitation to 
accumulate at the bottom of the clot ; and the white cor- 
puscles, being among the lightest constituents, collect in 
the upper part, and contribute to the formation of the 
buffy coat. 

The human red hlood-cells or blood corjmscles (figs. 25 and 
29) are circular flattened disks of different sizes, the majority 
varying in diameter from xoVo ^^ toV o" ^^ ^^ inch, and about 
TUo TTo" o^ ^^ i^^^ i^ thickness. When viewed singly, they 
appear of a pale yellowish tinge ; the deep red colour which 
they give to the blood being observable in them only when 
they are seen en masse. Their borders are rounded ; their 
surfaces, in the perfect and most usual state, slightly con- 
cave; but they readily acquire flat or convex surfaces 
when, the liquor sanguinis being diluted, they are swollen 
by absorption of fluid. They are composed of a colourless, 
structureless, and transparent filmy framework or stroma 
infiltrated in all parts by a red colouring-matter termed 
hmnoglobin. The stroma is tough and elastic, so that, as 
the cells circulate, they admit of elongation and other 
changes of form, in adaptation to the vessels, yet recover 
their natural shape as soon as they escape from compres- 
sion. The term cell, in the sense of a bag or sac, is inap- 
plicable to the red blood-corpuscle ; and it must be con- 

the case of the oval cells, only the long diameter is here given. It is 
remarkable, that although the size of the red blood-cells varies so much 
in the different classes of the vertebrate kingdom, that of the white 
corpuscles remains comparatively _uniform, and thus they are, in some 
animals, much greater, in others much less than the red corpuscles 
existing side by side with them. 

It may be here remarked, that the appearance of a nucleus in the red 
blood-cells of buxls, reptiles, amphibia and fish has been shown by Mr. 
Savory to be the result of post-mortem change ; no nucleus being 
visible in the cells as they circulate in the living body, or in those 
which have just escaped from the blood-vessels. 



72 THE BLOOD. 

sidered, if not solid throughout, yet as having no such 
variety of consistence in different parts as to justify the 
notion of its being a membranous sac with fluid contents. 
The stroma exists in all parts of its substance, and the 
colouring-matter uniformly pervades this, and is not merely 
surrounded by and mechanically enclosed within the outer 
wall of the corpuscle. The red corpuscles have no nuclei^ 
although, in their usual state, the unequal refraction of 
transmitted light gives the appearance of a central spot^ 
brighter or darker than the border, according as it is 
viewed in or out of focus. Their specific gravity is about 
1088. 

In examining a number of red corpuscles with a micro- 
scope, it is easy to observe certain natural diversities among 
them, though they may have been all taken from the same 
part. The great majority, indeed, are very uniform ; but 
some are rather larger, and the larger ones generally 
appear paler and less exactly circular than the rest ; their 
surfaces also are, usually, flat or slightly convex, they often 
contain a minute shining particle like a nucleolus, and they 
are lighter than the rest, floating higher in the fluid in 
which they are placed. Other deviations from the general 
characters assigned to the corpuscles, depend on changes 
that occur after they are taken from the body. Very com- 
monly they assume a granulated or mulberry-like form, in 
consequence, apparently, of a peculiar corrugation of their 
cell-walls. Sometimes, from the same cause, they present 
a very irregular, jagged, indented, or star-like appearance. 
The larger cells are much less liable to this change than 
the smaller, and the natural shape may be restored by 
diluting the fluid in which the corpuscles float ; by such 
dilution the corpuscles, as already said, may be made to 
swell up, by absorbing the fluid ; and, if much water be 
added, they will become spherical and pellucid, their 
colouring-matter being dissolved, and, as it were, washed 
out of them. Some of them may thus be burst ; the others 



BED BLOOD-CORPUSCLES. 73 

are made obscure ; but many of tbese latter may be brought 
into view again by evaporating, or adding saline matter to, 
the fluid, so as to restore it to its previous density. The 
changes thus produced by water are more quickly effected 
by weak acetic acid, which immediately makes the cor- 
puscles pellucid, but dissolves few or none of them, for 
the addition of an alkali, so as to neutralise the acid, will 
restore their form though not their colour. 

A peculiar property of the red corpuscles, which is exag- 
gerated in inflammatory blood, and which appears to exist 
in a marked degree in the blood of horses, may be here 
noticed. It gives them a great tendency to adhere together 
in rolls or columns, like piles of coins, and then, very 
quickly, these rolls fasten together by their ends, and 
cluster ; so that, when the blood is spread out thinly on a 
glass, they form a kind of irregular network, with crowds 
of corpuscles at the several points corresponding with the 
knots of the net (fig. 25). Hence, 
the clot formed in such a thin 
layer of blood looks mottled 
with blotches of pink upon a 
white ground : in a larger quan- 
tity of such blood, as soon as 
the corpuscles have clustered 
and collected in rolls (that is, 
generally in two or three minutes 
after the blood is drawn), they 

begin to sink very quickly ; for in the aggregate they pre- 
sent less surface to the resistance of the liquor sanguinis 
than they would if sinking separately. Thus, quickly sink- 
ing, they leave above them a layer of liquor sanguinis, 
and this coagulating, forms a buffy coat, as before de- 
scribed, the volume of which is augmented by the white 
corpuscles, which have no tendency to adhere to the red 
ones, and by their lightness float up clear of them. 

* Fig. 25. Eed corpuscles collected into rolls (after Henle). 




74 THE BLOOD. 

Chemical Composition of Red Blood-cells, 

It has been before remarked that the red blood-corpuscles 
are formed of a colourless stroma, infiltrated with a colour- 
ing matter termed licBmoglohin. As they exist in the 
blood they contain about three-fourths of their weight of 
water. 

The stroma appears to be composed of a nitrogenous 
proximate principle termed protagon, combined with albu- 
minous matter (paraglobulin or fibrinoplastin), fatty mat- 
ters including cholesterin, and salts, chiefly phosphates, of 
potash, soda and lime. 

Haemoglobin, which enters far more largely into the com- 
position of the red corpuscles than any other of their con- 
stituents, is allied to albumen in some respects, but differs 
remarkably from it in others. One of its most marked 
distinctive characters is its tendency under certain arti- 
ficial conditions to crystallize ; the so-called blood-crys- 
tals being but the natural crystalline forms assumed by 
this substance. 

Haemoglobin can be obtained in a crystalline form with 
various degrees of difficulty from the blood of different 
animals, that of man holding an intermediate place in this 
respect. Among the animals whose blood colouring-matter 
crystallizes most readilj^ are the guinea-pig and the dog ; 
and in these cases to obtain crystals it is generally suffi- 
cient to dilute a drop of recently drawn blood with water 
and expose it for a few minutes to the air. In many 
instances, however, a somewhat less simple process must be 
adopted; as the addition of chloroform or ether, rapid freezing 
and then thawing, or other means which separate the colour- 
ing-matter from the other constituents of the corpuscles. 

Different forms of blood-crystals are shown in the accom- 
panying figures. 

Another and most important character of haemoglobin is 
its attraction for oxygen, and some other gases, as carbonic 



BLOOD-CRYSTALS. 



75 



and nitrous oxides, with all of which it appears to form 
definite chemical combinations. The combination with 
oxygen is that which 



is of most physio- 
logical importance. 
During the passage 
of the blood through 
the lungs, it is con- 
stantly formed; while 
it is as constantly 
decomposed, in con- 
sequence of the rea- 
diness with which 
haemoglobin parts 
with oxygen, when 
the latter is exposed 
to other attractions 
in its circulation 
through the sys- 
temic capillaries. 
Thus, the red cor- 
puscles, in virtue of 
their colouring mat- 
ter, which readily 
absorbs oxygen and 
as readily gives it 
up again, are the 
chief means by which 
oxygen is carried in 
the blood (see also 
p. 85). 



Fig. 26.* 




Fig. 27.t 




* Figs. 26 , 27, and 28, ilhistrate some of the principal forms of 
blood-crystals : — 

Fig. 26, Prismatic, from human blood. 

t Fig. 27, Tetrahedral, from blood of the guinea-pig. 



76 



THE BLOOD. 



By lieat, mineral and otlier acids, 

Fig. 28.* 




alkalies, etc., iaeino- 
globin is decomposed 
into an albuminous 
matter (resembling 
globulin) and hcema- 
tln. The latter, now 
known to be a pro- 
duct of the decom- 
position of haemo- 
globin, was once 
thought to be the 
natural colouring 
matter of the blood. 



The White Corpuscles of the Blood or Blood Leucocytes. 

The white corpuscles are much less numerous than the 
red. On an average, in health, there may be one white 
to 400 or 500 red corpuscles ; but in disease, the propor- 
tion is often as high as one to ten, and sometimes even 
much higher. 

In health, the proportion varies considerably even in 
the course of the same day. The variations appear to 
depend chiefly on the amount and probably also on the 
kind of food taken ; the number of leucocytes being very 
considerably increased by a meal, and diminished again on 
fasting. 

They present greater diversities of form than the red 
ones do ; but the gradations between the extreme forms 
are so regular, that no sufiicient reason can be found for 
supposing that there is in healthy blood more than one 
species of white corpuscles. In their most general appear- 

* rig. 28, Hexagonal crystals from blood of squirrel. On these 
six-sided plates, prismatic crystals, grouped in a stellate manner, not 
iinfrequently occur (after Funke). 



WHITE BLOOD-CORPUSCLES. 



77 



ance, they are circular and nearly spherical, about ^"^^o tt of 
an inch, in diameter (fig. 29). They have a greyish, 
pearly look, appearing variously shaded or nebulous, the 
shading being much darker in some than in others. They 
seem to be formed of protoplasm (p. 19), containing 
granules which are in 

some specimens few and ^'^V- 29.* 

very distinct, in others 
(though rarely) so nu- 
merous that the whole 
corpuscle looks like a 
mass of granules. 

These corpuscles can- 
not be said to have any 
true cell- wall. In a few 
instances an apparent 
oell-membrane can be 
traced around them ; 

but, much more commonly, even this is not discernible till 
after the addition of water or dilute acetic acid, which 
penetrates the corpuscle, and lifts up and distends what 
looks like a cell-wall, to the interior of which the mate- 
rial, that before appeared to form the whole corpuscle, 
remains attached as the nucleus of the cell (fig. 29). 

A remarkable property of the white corpuscles, first 
observed by Mr. Wharton Jones, consists in their capa- 
bility of assuming different forms, irrespective of any 
external influence. If a drop of blood be examined 
with a high microscope power under conditions by which 
loss of moisture is prevented, at the same time that the 
temperature is maintained at about the degree natural to 
the blood as it circulates in the living body, the leu- 




* Fig. 29. Red and white blood-corpuscles. «, AVliitc corjjiiscle of 
natural aspect. J, Three white corpuscles acted on by weak acetic acid. 
< Red blood corpuscles. 



78 THE BLOOD. 

oocytes can be seen alternately contracting and dilating 
very slowly at various parts of their circumference, — shoot- 
ing out irregular processes, and again withdrawing them 
partially or completely, and thus in succession assuming 
various irregular forms. 

These movements, called amcehoid, from their resem- 
blance to the movements exhibited by an animal called 
the Amceha, the structure of which is as simple as that of 
a white blood-corpuscle, are characteristic of the living 
leucocyte, and form a good example of the contractile pro- 
perty of protoplasm, before referred to. Indeed, the unchang- 
ing rounded form which the corpuscles present in specimens 
of blood examined in the ordinary manner under the micro- 
scope, must be looked upon as the shape natural to a 
dead corpuscle, or one whose vitality is dormant, rather 
than as the proper shape of one living and active. 

Besides the red and white corpuscles, the microscope 
reveals numerous minute molecules or granules in the blood, 
circular or spherical, and varying in size from the most 
minute visible speck to the -^-^-^ of an inch (Gulliver). 
These molecules are very similar to those found in the 
lymph and chyle, and are, some of them, fatty, being 
soluble in ether, others probably albuminous, being soluble 
in acetic acid. Generally, also, there may be detected in 
the blood, especially during the height of digestion, very 
minute equal-sized fatty particles, similar to those of which 
the molecular base of chyle is constituted (Gulliver). 

The Serum, 

The serum is the liquid part of the blood remaining after 
the coagulation of the fibrin. In the usual mode of 
coagulation, part of the serum remains soaked in the clot, 
and the rest, squeezed from the clot by its contraction, lies 
around and over it. The quantity of serum that appears 
around the clot depends partly on the total quantity in the 
blood, but partly also on the degree to which the clot con- 



SERUM OF BLOOD. 



79 



tracts. This is affected by many circumstances : generally, 
the faster the coagulation the less is the amount of con- 
traction ; and, therefore, when blood coagulates quickly, it 
will appear to contain a small proportion of serum. Hence, 
the serum always appears deficient in blood drawn slowly into 
a shallow vessel, abundant in inflammatory blood drawn, into 
a tall vessel. In all cases, too, it should be remembered, that, 
since the contraction of the clot may continue for thirty-six 
or more hours, the quantity of serum in the blood cannot 
be even roughly estimated till this period has elapsed. 

The serum is an alkaline, slimy or viscid, yellowish fluid, 
often presenting a slight greenish, or greyish hue, and with 
a specific gravity of from 1025 to 1030. It is composed of 
a mixture of various substances dissolved in about nine 
times their weight of water. It contains, indeed, the 
greater part of all the substances enumerated as existing 
in the blood, with the exception of the fibrin and the red 
corpuscles. Its principal constituent is albumen, of which 
it contains about 8 per cent., and the coagulation of which, 
when heated, converts nearly the whole of the serum into 
a solid mass. The liquid which remains uncoagulated, 
and which is often enclosed in little cavities in the coagu- 
lated serum, is called serosity: it contains, dissolved in 
water, fatty, extractive, and saline matters. 

Variations in the principal Constituents of the Liquor Sanguinis. 

The ivater of the blood is subject to hourly variations in its 
quantity, according to the period since the taking of food, 
the amount of bodily exercise, the state of the atmosphere, 
and all the other events that may afi'ect either the ingestion 
or the excretion of fluids. According to these conditions, 
it may vary from 700 to 790 parts in the thousand. Yet 
uniformity is on the whole maintained; because nearly 
all those things which tend to lower the proportion of water 
in the blood, such as active exercise, or the addition of 
saline and other solid matter, excite thirst ; while, on the 



80 THE BLOOD. 

other hand, the addition of an excess of water to the blood 
is quickly followed by its more copious excretion in sweat 
and urine. And these means for adjusting the proportion 
of the water find their purpose in maintaining certain im- 
portant physical conditions in the blood ; such as its proper 
viscidity, and the degree of its adhesion to the vessels 
through which it ought to flow with the least possible 
resistance from friction. On this also depends, in great 
measure, the activity of absorption by the blood-vessels, 
into which no fluids will quickly penetrate, but such as are 
of less density than the blood. Again, the quantity of 
water in the blood determines chiefly its volume, and 
thereby the fulness and tension of the vessels and the 
quantity of fluid that will exude from them to keep the 
tissues moist. I'inally, the water is the general solvent of 
all the other materials of the liquor sanguinis. 

It is remarkable, that the proportion of water in the 
blood may be sometimes increased even during its abstrac- 
tion from an artery or vein. Thus Dr. Zimmerman in 
bleeding dogs, found the last drawn portion of blood 
contain 12 or 13 parts more of water in lOOQ than the 
blood first drawn; and Polli noticed a corresponding 
diminution in the specific gravity of the human blood 
during venesection, and suggested the only probable ex- 
planation of the fact, namely, that during bleeding, the 
blood-vessels absorb very quickly a part of the serous 
fluid with which all the tissues are moistened. 

The albumen may vary, consistently with health, from 60 
to 70 parts in the lOOO of blood. The form in which it 
exists in the blood is not yet certain. It may be that of 
simple solution as pure albumen : but it is, more probably, 
in combination with soda, as an albuminate of soda ; for, 
if serum be much diluted with water, and then neutralized 
with acetic acid, pure albumen is deposited. Another 
view entertained by Enderlin is that the albumen is dis- 
solved in the solution of the neutral phosphate of sodium. 



FATTY MATTERS IX THE BLOOD. 8 1 

to whicli lie considers the alkaline reaction of tlie blood to 
be due, and solutions of which can dissolve large quantities 
of albumen and phosphate of lime. 

The proportion of Jihrin in healthy blood may vary be- 
tween 2 and 3 parts in lOOO. In some diseases, such as 
typhus, and others of low type, it may be as little as i -034 ; 
in other diseases, it is said, it may be increased to as much 
as 7*528 parts in lOOO. But, in estimating the quantity 
of fibrin, chemists have not taken account of the white 
corpuscles of the blood. These cannot, by any mode of 
analysis yet invented, be separated from the fibrin of 
mammalian blood : their composition is unknown, but 
their weight is always included in the estimate of the 
fibrin. In health, they may, perhaps, add too little to its 
weight to merit consideration, but in many diseases, espe- 
cially in inflammatory and other blood diseases in which 
the fibrin is said to be increased, these corpuscles become 
so numerous that a large proportion of the supposed 
increase of the fibrin must be due to their being weighed 
with it. On this account all the statements respecting the 
increase of fibrin in certain diseases need revision. 

The enumeration of the fatty matters of the blood makes 
it probable that most of those which are found in the 
tissues or secretions exist also ready-formed in the blood ; 
for it contains the cholesterin of the bile, the cerebrin 
and phosphorised fat of the brain, and the ordinary saponi- 
fiable fats, stearin, olein, and palmatin. A volatile fatty 
acid is that on which the odour of the blood mainly de- 
pends; and it is supposed that when sulphuric acid is 
added (see p. 57), it evolves the odour by combining 
with the base with which, naturally, this acid is neutra- 
lized. According to Lehmann, much of the fatty matter of 
the blood is accumulated in the red corpuscles. 

These fatty matters are subject to much variation in 
quantity, being commonly increased after every meal in 
which fat, or starch, or saccharine substances have been 



82 THE BLOOD. 

taken. At such times, the fatty particles of the chyle, 
added quickly to the blood, are only gradually assimilated ; 
and their quantity may be sufficient to make the serum of 
the blood opaque, or even milk-like. 

As regards the inorganic constituents of the blood, — the 
substances which remain as ashes after its complete burning 
— one may observe in general their small quantity in pro- 
portion to that of the animal matter contained in it. 
Those among them of peculiar interest are the phosphate 
and carbonate of sodium, and the phosphate of calcium. 
It appears most probable, that the blood owes its alkaline 
reaction to both these salts of sodium. The existence of the 
neutral phosphate (Na2H.P04) was proved by Enderlin : 
the presence of carbonate of sodium has been proved by 
Lehmann and others. 

In illustration of the characters which the blood may 
derive from the phosphate of sodium, Liebig points out the 
large capacity which solutions of that salt have of absorb- 
ing carbonic acid gas, and then very readily giving it off 
again when agitated in atmospheric air, and when the 
atmospheric pressure is diminished. It is probably, also, 
by means of this salt, that the phosphate of calcium is held 
in solution in the blood in a form in which it is not soluble 
in water, or in a solution of albumen. Of the remaining 
inorganic constituents of the blood, the oxide and phos- 
phate of iron referred to, exist in the liquor sanguinis, 
independently of the iron in the corpuscles. 

Schmidt's investigations have shown that the inorganic 
constituents of the blood-ceUs somewhat differ from those 
contained in the serum ; the former possessing a consider- 
able preponderance of phosphates and of the salts of potas- 
sium, while the chlorides, especially of sodium, with phos- 
phate of sodium, are particularly abundant in the latter. 

Among the extractive matters of the blood, the most 
noteworthy are Creatin and Creatinin. Besides these, 
other organic principles have been found either constantly 



VAEIATIONS OF BLOOD. 



83 



or generally in the blood, including casein, especially in 
women during lactation : glucose, or grape-sugar, found in 
the blood of the hepatic vein, but disappearing during its 
transit through the lungs (Bernard); urea, and in very 
minute quantities, uric acid (Garrod) ; Jiippuric and lactic 
acids ; ammonia (Richardson) ; and lastly, certain colouring 
and odoriferous matters. 

Variations in healthy Blood under different Circumstances. 

As the general condition of the body depends so much 
on the condition of the blood, and as, on the other hand, 
anything that aJffects the body must sooner or later, and 
to a greater or less degree, affect the blood also, it might 
be expected that considerable variations in the qualities of 
this fluid would be found under different circumstances of 
disease ; and such is found to be the case. Even in health, 
however, the general comj)osition of the blood varies con- 
siderably. 

The conditions which appear most to influence the com- 
position of the blood in health, are these : sex, pregnancy, 
age, and temperament. The composition of the blood is 
also, of course, much influenced by diet. 

1. Sex. — The blood of men differs from that of women, 
chiefly in being of somewhat higher specific gravity, from its 
containing a relatively larger quantity of red corpuscles. 

2. Pregnancy. — The blood of pregnant women has a 
rather lower specific gravity than the average, from de- 
ficiency of red corpuscles. The quantity of white corpuscles, 
on the other hand, and of fibrin, is increased. 

3 . Age. — From the analysis of Denis it appears that the 
blood of the foetus is very rich in solid matter, and espe- 
cially in red corpuscles ; and this condition, gradually 
diminishing, continues for some weeks after birth. The 
quantity of solid matter then falls during childhood below 
the average, again rises during adult life, and in old age 
falls again. 

G 2 



84 THE BLOOD. 

4. Temperament. — But little more is known concerning 
tlie connection of this with, the condition of the blood, than 
that there appears to be a relatively larger quantity of solid 
matter, and particularly of red corpuscles, in those of a 
plethoric or sanguineous temperament. 

5. Diet. — Such differences in the composition of the 
blood as are due to the temporary presence of various 
matters absorbed with the food and drink, as well as the 
more lasting changes which must result from generous or 
poor diet respectively, need be here only referred to. 

Effects of Bleeding. — The result of bleeding is to diminish 
the specific gravity of the blood ; and so quickly, that in a 
single venesection, the portion of blood last drawn has often 
a less specific gravity than that of the blood that flowed 
first (J. Davy and PoUi). This is, of course, due to ab- 
sorption of fluid from the tissues of the body. The physio- 
logical import of this fact, namely, the instant absorption 
of liquid from the tissues, is the same as that of the intense 
thirst which is so common after either loss of blood, or the 
abstraction from it of watery fluid, as in cholera, diabetes, 
and the like. 

For some little time after bleeding, the want of red 
-blood-cells is weU marked; but, with this exception, no 
considerable alteration seems to be produced in the com- 
position of the blood for more than a very short time, the 
loss of the other constituents, including the pale corpuscles, 
being very quickly repaired. 

Variations in the Composition of the Blood, in different Parts 
of the Body. 

The composition of the blood, as might be expected, is 
found to vary in different parts of the body. Thus arterial 
blood differs from venous ; and although its composition 
and general characters are uniform throughout the whole 
course of the systemic arteries, they are not so throughout 



VAEIATIOXS OF BLOOD. 85 

tlie venous system, — the blood contained in some veins 
differing remarkably from that in others. 

I. Differences between arterial and venous blood. — These 
may be arranged under two heads, — differences in colour, 
and in general composition. 

a. Colour. — Concerning the cause of the difference in 
colour between arterial and venous blood, there has been 
much doubt, not to say confusion. For while the scarlet 
colour of the arterial blood has been supposed by some 
observers, and for some reasons, to be due to the chemical 
action of oxygen, and the purple tint of that in the veins 
to the action of carbonic acid, there are facts which made 
it seem probable that the cause was a mechanical one 
rather than a chemical, and that it depended on a difference 
in the shape of the red corpuscles, by which their power of 
transmitting and reflecting light was altered. Thus, car- 
bonic acid was thought to make the blood dark by causing 
the red cells to assume a bi-convex outline, and oxygen 
was supposed to reverse the effect by contracting them and 
rendering them bi-concave. We may believe, however, 
that, at least for the present, this vexed question has, by 
the results of investigations undertaken by Professor Stokes 
and others, been now set at rest. 

The colouring matter of the blood, or haemoglobin (p. 74), 
is capable of existing in two different states of oxidation, 
and the respective colours of arterial and venous blood are 
caused by differences in tint between these two varieties — 
oxidised or scarlet hcemoglobin and de-oxidised or purple 
haemoglobin. The change of colour produced by the passage 
of the blood through the lungs, and its consequent exposure 
to oxygen, is due, probably, to the oxidation of purple, 
and its conversion into scarlet haemoglobin; while the 
readiness with which the latter is de-oxidised offers a 
reasonable explanation of the change, in regard to tint, of 
arterial into venous blood, — the transformation being 
effected by the delivering up of oxygen to the tissues, by 



S6 THE BLOOD. 

the scarlet hemoglobin, during the blood's passage through 
the capillaries. The changes of colour are more probably- 
due to this cause, namely, a varying quantity of oxygen 
chemically combined with the haemoglobin, than to any 
mechanical effect of this gas, or to the influence of carbonic 
acid, either chemically, on the colouring matter, or me- 
chanically, on the corpuscles which contain it. We are 
not, perhaps, in a position to deny altogether the possible 
influence of mechanical conditions of the red corpuscles on 
the colour of arterial and venous blood respectively ; but it 
is probable that this cause alone would be quite insufficient 
to explain the differences in the colour of the two kinds of 
blood, and therefore if it be an element at all in the change, 
it must be allowed to take only a subordinate position. 

The distinction between the two kinds of haemoglobin 
naturally present in the blood, or, in other words, the 
proof that the addition or subtraction of oxygen involves 
the production respectively of two substances having funda- 
mental differences of chemical constitution, has been made 
out chiefly by spectrum- analysis, — the effects produced by 
placing oxidised and de-oxidised solutions of haemoglobin 
in the path of a ray of lig]^ traversing a spectroscope being 
different. For while th^^dised solution causes the ap- 
pearance of two absorption bands in the yellow and the 
green part of the sjjectrum, these are replaced by a single band 
intermediate in position, when the oxidised or scarlet solution 
is darkened by de-oxidising agencies, — or, in other words, 
when the change which naturally ensues in the conversion 
of arterial into venous blood is artificially produced.'^'^ 

The greater part of the haemoglobin in both arterial and 
venous blood probably exists in the scarlet or more highly 
oxidised condition, and only a small part is de -oxidised and 
made purple in its passage from the arteries into the veins. 

* The student to whom the terms employed in connection with 
spectrum analysis are not familiar, is advised to consult, with reference 
to the preceding paragi-aph, an elementary treatise on Physics. 



BLOOD OF rOETAL YEIX. 8/ 

The differences in regard to colour between arterial and 
venous blood are sometimes not to be observed. If blood 
runs very slowly from an artery, as from tbe bottom of a 
deep and devious wound, it is often as dark as venous 
blood. In persons nearly asphyxiated also, and some- 
times, under the influence of chloroform or ether, the 
arterial blood becomes like the venous. In the foetus 
also both kinds of blood are dark. But, in aU these cases, 
the dark blood becomes bright on exposure to the air. 
Bernard has shown that venous blood returning from a gland 
in active secretion is almost as bright as arterial blood. 

b. General Composition. — The chief differences between 
arterial and ordinary venous blood are these. Arterial 
blood contains rather more fibrin, and rather less albumen 
and fat. It coagulates somewhat more quickly. Also, it 
contains more oxygen, and less carbonic acid. According 
to Denis, the fibrin of venous blood differs from arterial, 
in that when it is fresh, and has not been much exposed 
to the air, it may be dissolved in a slightly heated solution 
of nitrate of potassium. 

Some of thj veins, however, contain blood which differs 
from the ordinary standard considerably. These are the 
portal, the hepatic, and the splenic veins. 

Portal vein. — The blood which the portal vein conveys 
to the liver is supplied from two chief sources ; namely, 
that in the gastric and mesenteric veins, which contains 
the soluble elements of food absorbed from the stomach 
and intestines during digestion, and that in the splenic 
vein ; it must, therefore, combine the qualities of the 
blood from each of these sources. 

The blood in the gastric and mesenteric veins will vary 
much according to the stage of digestion and the nature 
of the food taken, and can therefore be seldom exactly the 
same. Spaaking generally, and without considering the 
sugar, dextrine, and other soluble matters which may 
have been absorbed from the alimentary canal, this blood 



S8 THE BLOOD. 

appears to be deficient in solid matters, especially in red 
corpuscles, owing to dilution by the quantity of water ab- 
sorbed, to contain an excess of albumen, tbough cHefly of 
a lower kind than usual, resulting from the digestion of ni- 
trogenised substances, and termed albuminose, and to yield 
a less tenacious kind of fibrin than that of blood generally. 

The blood from the splenicvein is probably more definite 
in composition, though also liable to alterations according 
to the stage of the digestive process, and other circum- 
stances. It seems generally to be deficient in red cor- 
puscles, and to contain an unusually large proportion of 
albumen. The fibrin seems to vary in relative amount, 
but to be almost always above the average. The propor- 
tion of colourless corpuscles appears also to be unusually 
large. The whole quantity of solid matter is decreased, 
the diminution appearing to be chiefly in the proportion 
of red corpuscles. 

The blood of the portal vein, combining the peculiarities 
of its two factors, the splenic and mesenteric venous 
blood, is usually of lower specific gravity than blood 
generally, is more watery, contains fewer red corpuscles, 
more albumen, chiefly in the form of albuminose, and 
yields a less firm clot than that yielded by other blood, 
owing to the deficient tenacity of its fibrin. These 
characteristics of portal blood refer to the composition of 
the blood itself, and have no reference to the extraneous 
substances, such as the absorbed materials of the food, 
which it may contain ; neither, indeed, has any complete 
analysis of these been given. 

Comparative analyses of blood in the portal vein and 
blood in the hepatic veins have also been frequently made, 
with the view of determining the changes which this fluid 
undergoes in its transit through the liver. Great diversity, 
however, is observable in the analyses of these two kinds 
of blood by difierent chemists. Part of this diversity is no 
doubt attributable to the fact pointed out by Bernard, that 



GASES OF THE BLOOD. 89 

unless the portal vein is tied before the liver is removed 
from the body, hepatic venous blood is very liable to 
regurgitate into the portal vein, and thus vitiate the result 
of the analysis. Guarding against this source of error, 
recent observers seemed to have determined that hepatic 
venous blood contains less water, albumen, and salts, than 
the blood of the portal vein ; but that it yields a much 
larger amount of extractive matter, in which, according to 
Bernard and others, is one constant element, namely, grape- 
sugar, which is found, whether saccharine or farinaceous 
matter have been present in the food or not. 

Besides the rather wide difference between the composi- 
tion of the blood of these veins and of others, it must not be 
forgotten that in its passage through every organ and tissue 
of the body, the blood's composition must be varying con- 
stantly, as each part takes from it or adds to it such matter 
as it, roughly speaking, wishes either to have or to throw 
away. Thus the blood of the renal vein has been proved 
by experiment to contain less water than does the blood of 
the artery, and doubtless its salts are diminished also. The 
blood in the renal vein is said, moreover, by Bernard and 
Brown-Sequard not to coagulate. 

This then is an example of the change produced in the 
blood by its passage through a special excretory organ. But 
all parts of the body, bones, muscles, nerves, etc., must act 
on the blood as it passes through them, and leave in it some 
mark of their action, too slight though it may be, at any 
given moment, for analysis by means now at our disposal. 

On the Gases contained in the Blood. 

The gases contained in the blood are carbonic acid, 
oxygen, and nitrogen, lOO volumes of blood containing 
from 40 to 50 volumes of these gases collectively. 

Arterial blood contains relatively more oxygen and less 
carbonic acid than venous. But the absolute quantity of 
carbonic acid is in both kinds of blood greater than that of 



90 DEVELOPMENT OF BLOOD. 

the oxygen. The proportion of nitrogen is in both very- 
small. 

It is most probable that the carbonic acid of the blood 
is partly in a state of simple solution, and partly in a state 
of Treak chemical combination. The portion of the car- 
bonic acid which is chemically combined, is contained 
partly in a bicarbonate of soda, and partly is united with 
phosphate of the same base. The oxygen is combined 
chemically with the haemoglobin of the red corpuscles 
(pp. 75 and 85). 

That the oxygen is absorbed chiefly by the red corpuscles 
is proved by the fact that while blood is capable of 
absorbing oxygen in considerable quantity, the serum 
alone has little or no more power of absorbing this gas 
than pure water. 

Development of the Blood. 

In the development of the blood little more can be traced 
than the processes by which the corpuscles are formed. 

The first formed blood-cells of the human embryo differ 
much in their general characters from those which belong 
to the latter periods of intra-uterine, and to all periods of 
extra-uterine life. Their manner of origin differs also, 
and it will be well perhaps to consider this first. 

In the process of development of the embryo, the plan, 
so to speak, of the heart and chief blood-vessels is first 
laid out in cells. Thus the heart is at first but a solid 
mass of cells, resembling those which constitute all other 
parts of the embryo ; and continuous with this are tracts 
of similar cells — the rudiments of the chief blood-vessels. 

The formation of the first blood corpuscles is very 
simple. While the outermost of the embryonic cells, of 
which the rudimentary heart and its attendant vessels are 
composed, gradually develop into the muscular and other 
tissues which form the walls of the heart and blood-vessels, 
the inner cells simply separate from each other, and form 



DEVELOPMENT OF BLOOD. 



91 



blood-cells ; some fluid plasma being at the same time 
secreted. Thus, by the same process, blood is formed, and 
the originally solid heart and blood-vessels are hollowed out. 

The blood-cells i)roduced in this way, are from about 
23irTr *o ttW ^^ ^^ ^^^^ ^^ diameter, mostly spherical, 
pellucid, and colourless, with granular contents, and of 
well-marked nucleus. Gradually, they acquire a red 
colour, at the same time that the nucleus becomes more 
defined, and the granular matter clears away. Mr. Paget 
describes them, as, at this period, circular, thickly disc- 
shaped, full-coloured, and, on an average, about -a3-Vo of 
an inch in diameter ; their nuclei, which are about -5-0V0 ^^ 
an inch in diameter, are central, circular, very little pro- 
minent on the surfaces of the cell, and apparently slightly 
granular or tuberculated. 

Before the occurrence, however, of this change — from 
the colourless to the coloured state — in many instances, 
probably, during it, and in many afterwards, a process of 
multiplication takes place by division of the nucleus and 
subsequently of the cell, into two, and much more rarely, 






three or four new cells, which gradually acquire the 
characters of the original cell from which they sprang 
Fig. 30 (b, c, d, e). 

"^ Fig. 30. Develoi^ment of the first set of blood-corpuscles in the 



92 DEYELOrMEXT OF BLOOD. 

When, in the progress of embryonic development, the 
liver begins to be formed, the multiplication of blood- 
cells in the whole mass of blood ceases, according to 
Kolliker, and new blood-cells are produced by this organ. 
Like those just described, they are at first colourless and 
nucleated, but afterwards acquire the ordinary blood- 
tinge, and resemble very much those of the first set. Like 
them they may also multiply by division. In whichever 
way produced, however, whether from the original for- 
mative cells of the embryo, or by the liver, these coloured 
nucleated cells begin very early in foetal life to be mingled 
with coloured non-nucleated corpuscles resembling those of 
the adult, and about the fourth or fifth month of embryonic 
existence are completely replaced by them. 

The manner of origin of these perfect non-nucleated 
corpuscles must be now considered. 

I. Concerning the cells from which they arise. 

a. Before Birth. — It is uncertain whether they are 
derived only from the ceUs of the lymph, which, at about 
the period of their appearance, begins to be poured into 
the blood; or whether they are derived also from the 
nucleated red cells, which they replace, or also from similar 
nucleated cells, which Kolliker thinks are produced by the 
liver during the whole time of foetal existence. 

h. After Birth. — It is generally agreed that after birth the 
red corpuscles are derived from the smaller of the nucleated 
lymph or chyle-corpuscles, — the white corpuscles of the blood, 

II. Concerning the Manner of their Developnent. 

There is not perfect agreement among physiologists 

mammalian embryo. A. A dotted, nucleated embryo-cell in process of 
conversion into a blood-corpuscle ; the nucleus provided with a nucle- 
olus. B, A similar cell Avith a dividing nucleus ; at c, the division of 
the nucleus is complete ; at d, the cell also is dividing, e. A blood- 
corpuscle almost complete, but still containing a few granules, f. Per- 
fect blood-corpuscle. 



DEVELOPMENT OF BLOOD. 93 

concerning tlie process by which, lymph- globules or white 
corpuscles (and in the foetus, perhaps the red nucleated 
cells) are transformed into red non-nucleated blood-cells. 
For while some maintain that the whole cell is changed 
into a red one by the gradual clearing up of the con- 
tents, including the nucleus, it is believed by Mr. Wharton 
Jones and many others, that only the nucleus becomes the 
red blood-cell, by escaping from its envelope and acquiring 
the ordinary blood-tint. 

Of these two theories, that which supposes the nucleus 
of the lymph or chyle globule to be the germ of the future 
red blood-corpuscle is the theory now generally adopted. 

The development of red blood-cells from the corpuscles 
of the lymph and chyle continues throughout life, and 
there is no reason for supposing that after birth they have 
any other origin. 

Without doubt, these little bodies have, like all other 
parts of the organism, a tolerably definite term of existence, 
and in a like manner die and waste away ivhen the portion 
of work allotted to them has been performed. Neither the 
length of their life, however, nor the fashion of their 
decay, has been yet clearly made out, and we can only 
surmise that in these things they resemble more or less 
closely those parts of the body which lie more plainly 
within our observation. 

From what has been said, it will have appeared that when 
the blood is once formed, its growth and maintenance are 
effected by the constant repetition of the development of 
new portions. In the same proportion that the blood yields 
its materials for the maintenance and repair of the several 
solid tissues, and for secretions, so are new materials sup- 
plied to it in the lymph and chyle, and by devdopment 
made like it. The part of the process which relates to the 
formation of new corpuscles has been described, but it is 
probably only a small portion of the whole process ; for the 
assimilation of the new materials to the blood must be 



94 ASSIMILATIOX OF ELOOD. 

perfect, in regard to all those immeasurable minute par- 
ticulars by which the blood is adapted for the nutrition of 
every tissue, and the maintenance of every peculiarity of 
each. How precise the assimilation must be for such an 
adaptation, may be conceived from some of the cases in 
which the blood is altered by disease, and by assimilation 
is maintained in its altered state. For example, by the 
insertion of vaccine Inatter, the blood is for a short time . 
manifestly diseased ; however minute the portion of virus, 
it affects and alters, in some way, the whole of the blood. 
And the alteration thus produced, inconceivably slight as 
it must be, is long maintained ; for even very long after a 
successful vaccination, a second insertion of the virus may 
have no effect, the blood being no longer amenable to its 
influence, because the new blood, formed after the vaccina- 
tion, is made like the blood as altered by the vaccine 
virus ; in other words, the blood exactly assimilates to its 
altered self the materials derived from the lymph and chyle. 
In health we cannot see the precision of the adjustment 
of the blood to the tissues ; but we may imagine it from 
the small influences by which, as in vaccination, it is 
disturbed ; and we may be sure that the new blood is as 
perfectly assimilated to the healthy standard as in disease 
it is assimilated to the most minutely altered standard.* 

How far the assimilation of the blood is affected by any 
formative power which it may possess in common with the 
solid tissues, we know not. That this possible formative 
power is, however, if present, greatly ministered to and 
assisted by the actions of other parts there can be no doubt ; 
as 1st, by the digestive and absorbent systems, and pro- 
bably by the liver, and all of the so-called vascular glands ; 
and, 2ndly, by the excretory organs, which separate from 
the blood refuse materials, including in this term not only 



* Corresponding facts in relation to the maintenance of the tissues 
by assimilation will be mentioned in the chapter on Xuteitiox . 



USES OF THE ELOOD. 



95 



the waste substance of tlie tissues, but also sucb matters 
as, having been taken with food and drink, may have been 
absorbed from the digestive canal, and have been sub- 
sequently found unfit to remain in the circulating current. 
And, ^rdhj, the precise constitution of the blood is adjusted 
by the balance of the nutritive processes for maintaining 
the several tissues, so that none of the materials appro- 
priate for the maintenance of any part may remain in 
excess in the blood. Each part, by taking from the blood 
the materials it requires for its maintenance, is, as has 
been observed, in the relation of an excretory organ to all 
the rest ; inasmuch as by abstracting the matters proper 
for its nutrition, it prevents excess of such matters as 
effectually as if they were separated from the blood and 
cast out altogether by the excreting organs specially present 
for such a purpose. 

Uses of the Blood. 

The purposes of the blood, thus developed and main- 
tained, appear, in the perfect state, to be these; ist, to be 
a source whenco the various parts of the body may abstract 
the materials necessary for their nutrition and mainte- 
nance; and whence the secreting organs may take the 
materials for their various secretions; 2nd, to be a 
constantly replenished store-house of latent chemical force, 
which in its expenditure will maintain the heat of the 
body, or be transformed by the living tissues, and mani- 
fested by them in various forms as vital power ; ^rd, to 
convey oxygen to the several tissues which may need it, 
either for the discharge of their functions, or for combination 
with their refuse matter ; ^th, to bring from all parts refuse 
matters, and convey them to places whence they may be dis- 
charged ; 5^^, to warm and moisten all parts of the body. 



of the various Constituents of the Blood. 
Kegarding the uses of the various constituents of the 



96 USES OF THE BLOOD. 

blood it may be said that the matter almost resolves itself 
into an analysis of the different parts of the body, and of 
the food and drink which are taken for their nutrition, 
with a subsequent consideration of how far any given con- 
stituent of the blood may be supposed to be on its way 
to the living tissues, to be incorporated with and nourish 
them, or, having fulfilled its purpose, to be on its way in a 
more or less changed condition to the excretory organs to be 
cast out. It must be remembered, however, that the blood 
contains also matters which serve by their combustion 
to produce heat, and, again, others which possibly sub- 
serve only a mechanical, although most important, purpose ; 
as for instance the preservation of the due specific gravity 
of the blood, or some other quality by which it is enabled 
to maintain its proper relation to the vessels containing it 
and to the tissues through which it passes. Lastly, among 
the constituents of the blood, are the gases, oxygen and 
carbonic acid, and the substances specially adapted to carry 
them, which can scarcely be said to take part in the nutri- 
tion of the body, but are rather the means and evidence of 
the combustion before referred to, on which, to a great 
extent, directly or indirectly, all vitality depends. 

Albumen. — The albumen, which exists in so large a 
proportion among the chief constituents of the blood, is 
without doubt mainly for the nourishment of those tex- 
tures which contain it or other compounds nearly allied to it. 
Besides its purpose in nutrition, the albumen of the liquor 
sanguinis is doubtless of importance also in the maintenance 
of those essential physical properties of the blood to which 
reference has been already made. 

Fibrin. — It has been mentioned in a previous part of 
this chapter that the idea of fibrin existing in the blood, 
as fibrin, is probably founded in error ; and that it is formed 
in the act of coagulation by the union of two substances, 
which before existed separately (p. 64). In considering, 
therefore, the functions of fibrin, we may exclude the notion 



USES OF BLOOD. 97 

of its existence, as sucli, in the blood in a fluid state, and of 
its use in the nutrition of certain special textures, and look 
for the explanation of its functions to those circumstances, 
whether of health or disease, under which it is produced. 
In haemorrhage, for example, the formation of fibrin in the 
clotting of blood, is the means by which, at least for a 
time, the bleeding is restrained or stopped; and the material 
which is produced for the permanent healing of the injured 
part, contains a coagulable material probably identical, or 
very nearly so, with the fibrin of clotted blood. 

Fatty Matters. — The fatty matters of the blood subserve 
more than one purpose. For while they are the means, at 
least in part, by which the fat of the body, so widely dis- 
tributed in the proper adipose and other textures, is re- 
plenished, they also, by their union with oxygen, assist in 
maintaining the temperature of the body. In certain secre- 
tions also, notably the milk and bile, fat is an important 
constituent. 

Saline Matter. — The uses of the saline constituents of 
the blood are, first, to enter into the composition of such 
textures and secretions as naturally contain them, and, 
secondly, to assist in preserving the due specific gravity 
and alkalinity of the blood and, perhaps, also in preventing 
its decomposition. The phosphate and carbonate of sodium, 
besides maintaining the alkalinity of the blood, are said 
especially to preserve the liquidity of its albumen, and to 
favour its circulation through the capillaries, at the same 
time that they increase the absorptive power of the serum 
for gases. But although, from the constant presence of a 
certain quantity of saline matter in the blood, we may 
believe that it has these last-mentioned imp'ortant functions 
in connection with the blood itself, apart from the nutri- 
tion of the body, yet, from the amount which is daily 
separated by the difi'erent excretory organs,' and especially 
by the kidneys, we must also believe that a considerable 
quantity simply passes through the blood, both from the 



98 USES OF BLOOD. 

food and from the tissues, as a temporary and useless con - 
stituent, to be excreted when opportunity offers. 

Corpuscles. — The uses of the red corpuscles are probably 
not yet fully known, but they may be inferred, at least in 
part, from the composition and properties of their contents. 
The affinity of haemoglobin for oxygen has been already 
mentioned ; and the main function of the red corpuscles 
seems to be the absorption of oxygen in the lungs by 
means of this constituent, and its conveyance to all parts of 
the body, especially to those tissues, the nervous and mus- 
cular, the discharge of whose functions depends in so great 
a degree upon a rapid and full supply of this element. 
The readiness with which haemoglobin absorbs oxygen, and 
delivers it up again to a reducing agent, so well shown by 
the experiments of Prof. Stokes, admirably adapts it for 
this purpose. How far the red corpuscles are concerned 
in the nutrition of the tissues is quite unknown. 

The relation of the white to the red corpuscles of the 
blood has been abeady considered (p. 92) ; of the functions 
of the former, other than are concerned in this relationship, 
nothing is positively known. Recent observations of the 
migration of the white corpuscles from the interior of the 
blood-vessels into the surrounding tissues (see Section, On 
the Circulation in the Capillaries) have, however, opened 
out a large field for investigation of their probable func- 
tions in connection with the nutrition of the textures, 
in which, even in health, they appear to wander. 



THE CmCULATIOX. 99 

CHAPTER YI. 

CIRCXJLATIOX OF THE BLOOD. 

The body is divided into two chief cavities — the chest or 
thorax and abdomen, by a curved muscular partition, called 
the diaphragm (fig. 31). The chest is almost entirely filled 
by the lungs and heart ; the latter being fitted in, so to 
speak, between the two lungs, nearer the front than 
the back of the chest, and partly overlapped by them 
(fig. 31). Each of these organs is contained in a distinct 
bag, called respectively the right and left pleura and the 
pericardium, the latter being fibrous in the main, but lined 
on the inner aspect by a smooth shining epithelial covering, 
on which can glide, with but little friction, the equally 
smooth surface of the heart enveloped by it. In fig. 3 1 
the containing bags of pleura and pericardium are sup- 
posed to have been removed. Entering the chest firom 
above is a Irrge and long air-tube, called the trachea, 
which divides into two branches, one for each lung, and 
through which air passes and repasses in respiration. 
Springing from the upper part or base of the heart may be 
seen the large vessels, arteries, and veins, which convey 
blood either to or from this organ. 

In the living body the heart and lungs are in constant 
rhythmic movement, the result of which is an unceasing 
stream of air through the trachea alternately into and out 
of the lungs, and an unceasing stream of blood into and 
out of the heart. 

It is with this last event that we are concerned especially 
in this chapter, — with the means, that is to say, by which 
the blood which at one moment is forced out of the heart, 
is in a few moments more returned to it, again to depart, 
and again pass through the body in course of what is 

II 2 



lOO 



THE CIKCULATIOX. 



technically called the circulation. The purposes for which 
this unceasing current is maintained, are indicated in the 
uses of the blood enumerated in the preceding chapter. 

The blood is conveyed away from the heart by the 
arteries, and returned to it by the veins ; the arteries and 
reins being continuous with each other, at one end by 
means of the heart, and at the other by a fine network of 
vessels called the capillaries. The blood, therefore, in its 
passage from the heart passes first into the arteries, then 
into the capillaries, and lastly into the veins, by which it 
is conveyed back again to the heart, — thus completing a 
revolution, or circulation. 



Fig. zi.' 




Right 
Lung. 



As generally described there are two circulations by 
which all the blood must pass ; the one, a shorter circuit 



* Fig. 31. View of heart and Imxga in situ. The front portion of 
the chest-Avall, and tlie outer ov 2Mri€tal layers of the pleurce and peri- 
cardium have been removed. The lungs are partl}^ collapsed. 



THE CIRCULATIOX. 



lOI 



firom the heart to the lungs and back again ; the other and 
larger circuit, from the heart to all parts of the body and 
back again ; but more strictly speaking, there is only one 
complete circulation, which may be diagrammatically repre- 
sented by a double loop, as in the accompanying figure. 



Fig. 32. 



On reference to 
this figure and 
noticing the di- 
rection of the ar- 
rows which repre- 
sent the course 
of the stream 
of blood, it will 
be observed that 
while there is a 
smaller and a 
larger circle both 
of which pass 
through the heart, 
yet that these are 
not distinct, one 
from the other, 
but are formed 
really by one con- 
tinuous stream, 
the whole of 
which must, at 
one part of 'its course, pass through the lungs. Subor- 
dinate to the two principal circulations, the imlmonary and 
systemic as they are named, it will be noticed also in the 
same figure, that there is another, by which a portion 
of the stream of blood having been diverted once into 
the capillaries of the intestinal canal, and some other 
organs, and gathered up again into a single stream, is a 
second time divided in its passage through the liver. 




Fig, 32. Diagram of the circulation. 



I02 THE CIECULATIOX. 

before it finally' reaches the heart and completes a revolu- 
tion. This subordinate stream through the liver is called 
the portal circulation. 

The principal force provided for constantly moving the- 
blood through this course is that of the muscular substance 
of the heart ; other assistant forces are (2) those of the 
elastic walls of the arteries, (3) the pressure of the muscles 
among which some of the veins run, (4) the movements of 
the walls of the chest in respiration, and probably, to soma 
extent, (5), the interchange of relations between the blood 
and the tissues which ensues in the capillary system during 
the nutritive processes. The right direction of the blood's 
course is determined and maintained by the valves of the 
heart to be immediately described ; which valves open to- 
permit the movement of the blood in the course described, 
but close when any force tends to move it in the contrary 
direction. 

We shall consider separately each member of the system 
of organs for the circulation : and first — 

The Heart. 
The heart is a hollow muscular organ, the interior of 
which is divided by a partition in such a manner as to 
form two chief chambers as cavities — right and left. Each 
of these chambers is again subdivided into an upper and 
a lower portion called respectively the auricle and ventricle^ 
which freely communicate one with the other ; the aperture 
of communication, however, being guarded by valvular 
curtains, so disposed so as to allow blood to pass freely from 
the auricle into the ventricle, but not in the opposite direc- 
tion. There are thus four cavities altogether in the heart 
— two auricles and two ventricles ; the auricle and ventricle- 
of one side being quite separate from those of the other. 
The right auricle commimicates, on the one hand, with the 
veins of the general system, and, on the other, with the 
right ventricle, while the latter leads directly into the pul- 
monary artery, the orifice of which is guarded by valves. 



THE HEART. 



103 



The left auricle again commumcates, on tlie one hand, with 
the pulmonary veins, and on the other, with the left 
ventricle, while the latter leads directly into the aorta — a 
large artery which conveys blood to the general system, 
the orifice of which, like that of the pulmonary artery, is 
guarded by valves. 

The arrangement of the heart's valves is such that 
the blood can pass only in one definite direction, and 
this is as follows (fig. 33): — From the right auricle 
the blood passes into the right ventricle, and thence 
into the pulmo- 
nary artery, by 
which it is con- 
veyed to the ca- 
pillaries of the 
lungs. From the 
lungs the blood, 
. which is nowpuri- 
fied and altered 
in colour, is ga- 
thered by the pul- 
monary veins and 
taken to the left 
auricle. From the 
left auricle it 
passes into the 
left ventricle, and 
thence into the 
aorta, by which it is distributed to the capillaries of every 
portion of the body. The branches of the aorta, from 
being distributed to the general system, are called systemic 
arteries ; and from these the blood passes into the sys- 
temic capillaries, where it again becomes dark and impure, 
and thence into the branches of the sijstemic veins, which 




Fig- 33. Diagram of the circulation tlirougli the heart (after Dalton) 



104 



THE CIRCULATION. 



forming by their union two large trunks, called tlie supe- 
rior and inferior vena cava, discharge their contents into 
the right auricle, whence we supposed the blood to start 

(fig- 33). 

Structure of the Valves of the Heart. 
It will be well now to consider the structure of the 




* Fig. 34. The right auricle and ventricle opened, and a part of 
their right and anterior walls removed, so as to show their interior, J. 
— I, superior vena cava ; 2, inferior vena cava ; 2', hepatic veins cut 
short ; 3, right auricle ; 3', placed in the fossa ovalis, below which is 
the Eustachian valve ; 3", is placed close to the aperture of the coronary 



STRUCTUEE OF HEART'S VALVES. 105 

valves of the heart, and the manner in which they perform 
their function of directing the stream of blood in the 
course which has been just described. The valve between 
the right auricle and ventricle is named tricuspid (fig. 34), 
because it presents three principal cusps or pointed portions, 
and that between the left auricle and ventricle bicuspid or 
mitral, because it has two such portions (fig. 35). But in 
both valves there is between each two principal portions a 
smaller one ; so that more properly, the tricuspid may be 
described as consisting of six, and the mitral of four, por- 
tions. Each portion is of triangular form, its apex and 
sides lying free in the cavity of the ventricle, and its base, 
which is continuous with the bases of the neighbouring 
portions, so as to form an annular membrane around the 
auriculo-ventricular opening, being fijxe'd to a tendinous 
ring, which encircles the orifice between the auricle and 
ventricle, and receives the insertions of the muscular fibres 
of both. In each principal portion of the valve may be 
distinguished a middle-piece, extending from its base to 
its apex, and including about half its width; this piece 
is thicker, aud much tougher and tighter than the border- 
pieces which are attached loose and flapping at its sides. 

While the bases of the several portions of the valves 
are fixed to the tendinous rings, their ventricular surfaces 



vein ; + , + , placed in the auriciilo- ventricular gi'oove, where a narrow 
portion of the adjacent walls of the auricle and ventricle has been pre- 
sei"ved ; 4, 4, cavity of the right ventricle, the upper figure is imme- 
diately below the semilunar valves ; 4', large columna carnea or mus- 
€ulus papillaris ; 5, 5', 5", tricuspid valve ; 6, placed in the interior of 
the pulmonary artery, a part of the anterior wall of that vessel having 
been removed, and a narrow portion of it preserved at its commence - 
Tuent where the semilunar valves are attached ; 7, concavity of the aortic 
arch close to the cord of the ductus arteriosus ; 8, ascending part or 
sinus of the arch covered at its commencement by the auricular appendix 
and pulmonary artery ; 9, placed between the innominate and left carotid 
arteries ; 10, appendix of the left auricle ; ii, ii, the outside of the left 
ventricle, the lower figure near the apex. (From Quain's Anatomy.) 



io6 



THE CIRCULATION. 



and borders are fastened by slender tendinous fibres, the 
chordm tendinecB, to the walls of the ventricles, the muscular 
fibres of which project into the ventricular cavity in the 

Fig. 35-* 




* Fig. 35, The loft auricle and ventricle opened and a part of their 
anterior and left ■walls removed so as to show their interior, i. — The 
pulmonary artery has been divided at its commencement so as to show 
the aorta ; the opening into the left ventricle has been carried a short 
distance into the aorta between two of the segments of the semilunar 
valves ; the left part of the auricle with its appendix has been removed. 



STRUCTURE OF HEART'S VALVES. lo/ 

form of bundles or columns — the columns carnecB. These 
columns are not all of them alike, for while some of them 
are attached along their whole length on one side, and 
by their extremities, others are attached only by their 
extremities ; and a third set, to which the name musculi 
pajnllares has been given, are attached to the wall of the 
ventricle by one extremity only, the other projecting, 
papilla-like, into the cavity of the ventricle (5, fig. 35)> ^^^ 
having attached to it cJiordcc tendinem. Of the tendinous 
cords, besides those which pass from the walls of the ven- 
tricle and the musculi ixqnllares, to the margins of the valves 
both free and attached, there are some of especial strength, 
which pass from the same parts to the edges of the middle 
pieces of the several chief portions of the valve. The 
ends of these cords are spread out in the substance of the 
valve, giving its middle piece its peculiar strength and 
toughness; and from the sides numerous other more 
slender and branching cords are given off, which are 



The right auricle has been thrown out of view, i, the two right pul- 
monary veins cut short ; their openings are seen -within the auricle ; 
i', placed within the cavit}' of the auricle on the leftside of the septum 
and on the part which forms the remains of the valve of the foi-amen 
ovale, of which the crescentic fold is seen towards the left hand of i' ; 
2, a narrow portion of the wall of the auricle and ventricle preserved 
round the auriculo-ventiicular orifice ; 3, 3', the cut surface of the walls 
of the ventricle, seen to become very much thinner towards 3", at the 
apex ; 4, a small part of the anterior wall of the left ventricle which 
has been preserved Avith the principal anterior columna carnea or 
musculus papillaris attached to it; 5, 5, musculi papillares ; 5', the 
left side of the septum between the two ventricles, within the cavity of 
the left ventricle ; 6, 6', the mitral valve ; 7, placed in the interior of 
the aorta near its commencement and above the three segments of its 
semilunar valve which are hanging loosely together ; 7', the exterior of 
the gi-eat aortic sinus ; 8, the root of the i>uhnonary arteiy and its 
semilunar valves ; 8', the separated portion of the pulmonary artery 
remaining attached to the aorta by 9, the cord of the ductus arteriosus ; 
10, the arteries rising from the summit of the aortic arch. (From 
Quain's Anatomy.) 



f08 THE CIHCULATIOX. 

attached all over the ventricular surface of the adjacent 
border-pieces of the principal portions of the valves, as 
well as to those smaller portions which have been mentioned 
as lying between each two principal ones. Moreover, the 
mmculi j^cfpUlares are so placed that from the summit of 
each tendinous cords may proceed to the adjacent halves of 
two of the princij)al divisions, and to one intermediate or 
smaller division, of the valve. 

It has been already said that while the ventricles com- 
municate, on the one hand, with the auricles, they commimi- 
cate, on the other, with the large arteries which convey the 
blood away from the heart; the right ventricle with the pul- 
monary artery (6, fig. 34), which conveys blood to the lungs, 
and the left ventricle with the aorta, which distributes it 
to the general system (7, fig. 35). And as the auriculo- 
ventricular orifice is guarded by valves, so are also the 
mouths of the pulmonary artery and aorta (figs. 34, 35). 

The valves, three in number, which guard the orifice of 
each of these two arteries, are called the semilunar valves. 
They are nearly alike on both sides of the heart ; but those 
of the aorta are altogether thicker and more strongly con- 
structed than those of the pulmonary artery. Like the 
tricuspid and mitral valves, they are formed by a dupli- 
cature of the lining membrane of the heart, strengthened 
by fibrous tissue. Each valve is of semilunar shape, its 
convex margin being attached to a fibrous ring at the 
place of junction of the artery to the ventricle, and the 
concave or nearly straight border being free (fig. 35). In 
the centre of the free edge of the valve, which contains a 
fine cord of fibrous tissue, is a small fibrous nodule, the 
corpus Arantii, and from this and from the attached border . 
fine fibres extend into every part of the mid substance of 
the valve, except a small lunated space just within the 
free edge, on each side of the corpus Arantii. Here the 
valve is thinnest, and composed of little more than the 
endocardium. Thus constructed and attached, the three 



ACTION OF THE HEART. 



109 



semilunar valves are placed side by side around the arterial 
orifice of each ventricle, so as to form three little pouches, 
which can be thrown back and flattened by the blood pass- 
ing out of the ventricle, but which belly out immediately 
so as to prevent any return (6, fig. 34). This will be again 
referred to immediately. 

The muscular fibres of the heart, unlike those of most 
involuntary muscles, present a striated appearance under 
the microscope. (See Chapter on Motion.) 

THE ACTION OF THE HEART. 

The heart's action in propelling the blood consists in the 
successive alternate contractions and dilatations of the mus- 
cular walls of its two auricles and two ventricles. Th© 
auricles contract simultaneously ; so do the ventricles ; their 
dilatations also are severally simultaneous ; and the con- 
tractions of the one pair of cavities are synchronous with 
the dilatations of the other. 

The description of the action of the heart may best be 
commenced at that period in each action which immediately 
precedes the beat of the heart against the side of the chest, 
and, by a very small interval more, precedes the pulse at 
the wrist. For at this time the whole heart is in a passive 
state, the walls of both auricles and ventricles are relaxed,, 
and their cavities are being dilated. The auricles are 
gradually filling with blood flowing into them from the 
veins ; and a portion of this blood passes at once through 
them into the ventricles, the opening between the cavity 
of each auricle and that of its corresponding ventricle 
being, during all the pause, free and patent. The auricles, 
however, receiving more blood than at once passes through 
them to the ventricles, become, near the end of the pause, 
fully distended ; then, in the end of the pause, they con- 
tract and empty their contents into the ventricles. The | 
contraction of the auricles is sudden and very quick ; it \ 
commences at the entrance of the great veins into them, 



no THE CIRCULATIOX. 

and is thence propagated towards tlie aricnlo-ventricular 
opening ; but the last part which contracts is the aricular 
appendix. The effect of this contraction of the auricles is 
to propel nearly the whole of their blood into the ventricles. 
! The reflux of blood into the great veins is resisted not only 
by the mass of blood in the veins and the force with which 
it streams into the auricles, but also by the simultaneous 
contraction of the muscular coats with which the large 
veins are provided for some distance before their entrance 
into the auricles ; a resistance which, however, is not so 
complete but that a small quantity of blood does regurgi^ 
tate, i.e., flow backwards into the veins, at each auricular 
contraction. The effect of this regurgitation from the 
I right auricle is limited by the valves at the junction of the 
) subclavian and internal jugular veins, beyond which the 
I blood cannot move backwards ; and the coronary vein, or 
, vein which brings back to the right auricle the blood 
I which has circulated in the substance of the heart, is pre- 
served from it by a valve at its mouth. 

The blood which is thus driven, by the contraction of the 
auricles, into the corresponding ventricles, being added to 
that which had already flowed into them during the heart's 
pause, is sufficient to complete the dilatation or diastole of 
the ventricles. Thus distended, they immediately contract : 
so immediately, indeed, that their contraction, or systole, 
looks as if it were continuous with that of the auricles. 
This has been graphically described by Harvey in the 
following passage : — " These two motions, one of the ven- 
tricles, another of the auricles, take place consecutively, 
but in such a manner that there is a kind of harmony, or 
rhythm, present between them, the two concurring in such 
wise-that but one motion is apparent ; especially in the 
warmer blooded animals, in which the movements in ques- 
tion are rapid. Nor is this for any other reason than it is 
in a piece of machinery, in which, though one wheel gives 
motion to another, yet all the wheels seem to move simul- 



ACTIOX OF THE HEART. iii 

taneously; or in that mechanical contrivance which is 
adapted to fire-arms, where the trigger being touched, 
down comes the flint, strikes against the steel, elicits a 
spark, which, falling among the powder, it is ignited, upon 
which the flame extends, enters the barrel, causes the 
explosion, propels the ball, and the mark is attained — all 
of which incidents ^ by reason of the celerity with which 
they happen, seem to take place in the twinkling of an 
eye." The ventricles contract much more slowly than 
the auricles, and in their contraction, probably always 
thoroughly empty themselves, differing in this respect from 
the auricles, in which even after their complete contrac- 
tion, a small quantity of blood remains. The form and 
position of the fleshy columns on the internal walls of the 
ventricle appear, indeed, especially adapted to produce this 
obliteration of their cavities during their contraction; and the 
completeness of the closure may often be observed on making 
a transverse section of a heart shortly after death, in any case 
in which the contraction of the rigor mortis is very marked. 
In such a case, only a central fissure may be discernible to 
the eye in the place of the cavity of each ventricle. 

At the same time that the walls of the ventricles con- 
tract, the fleshy columns, and especially those of them 
called the muscuU papillares, contract also, and assist in 
bringing the margins of the auriculo-ventricular valves 
into apposition, so that they close the auriculo-ventricular 
openings, and prevent the backward passage of the blood 
into the auricles (p. 1 13). The whole force of the ven- 
tricular contraction is thus directed to the propulsion of 
the blood through their arterial orifices. During the time 
which elapses between the end of one contraction of the 
ventricles, and the commencement of another, the com- 
munication between them and the great arteries — the aorta 
on the left side, the pulmonary artery on the right — is 
closed by the three semilunar valves situated at the orifice 
of each vessel. But the force with which the current of 



1 1 2 THE CIECULATIOX. 

blood is propelled by the contraction of the ventricle sepa- 
rates these valves from contact with each other, and presses 
them back against the sides of the artery, making a free 
passage for the stream of blood. Then, as soon as the ven- 
tricular contraction ceases, the elastic walls of the distended 
artery recoil, and, by pressing the blood behind the valves, 
force them down towards the centre of the vessel, and spread 
them out so as to close the orifice and prevent any of the 
blood flowing back into the ventricles (p. Ii8). 

As soon as the auricles have completed their contraction 
they begin again to dilate, and to be refilled with blood, 
which flows into them in a steady stream through the 
great venous trunks. They are thus filling during all the 
time in which the ventricles are contracting ; and the con- 
traction of the ventricles being ended, these also again 
dilate, and receive again the blood that flows into them 
from the auricles. By the time that the ventricles are 
thus from one -third to two-thirds full, the auricles are 
distended; these, then suddenly contracting, fill up the 
ventricles, as already described. 

If we suppose a cardiac revolution, which includes the 
contraction of the auricles, the contraction of the ventricles, 
and their repose, to occupy rather more than a second, the 
following table will represent, in tenths of a second, the 
time occupied by the various events we have considered. 

Contraction of Auricles . . i + Eepose of Auricles . , io=ii 
,, Ventricles . 4+ ,, Ventricles . 7=11 

Eepose (no contraction of . 
eitlier auricles or ventricles) 6 + Contraction (of either 

— auricles or ventricles) 5 = ii 
II 

Action of the Valves of the Heart. 

The periods in which the several valves of the heart are 

in action may be connected with the foregoing table ; for 

the auriculo-ventricular valves are closed, and the arterial 

valves are open during the whole time of the ventricular 

contraction, while, during the dilatation and distension of 



FUXCTIOX OF THE VALVES. 



113 



the ventricles the latter valves are shut, the former open. 
Each half or side of the heart, through the action of its 
valves, may be ^-^ .5 * 

compared with a 
kind of forcing 
pump like the 
common enema- 
syringe with two 
valves, of which 
one admits the 
fluid on raising 
the piston, but 
is closed again 
when the piston 
is forced down ; 
while the other 
opens for the es- 
cape of the fluid, 
but closes when 
the piston is 
raised, so as to 
prevent the re- 
gurgitation of the 
fluid already 
forced through it. 
The ventricular 
dilatation is here 
represented by 
the raising-up of 
the piston ; the 
valve thus admit- 
ting fluid repre- 
sents the auriculo- 
ventricular valve, 
which is closed 




Fig. 36. Diagrams of valves of the heart (after Dalton). 



114 THE CIRCULATIOX. 

again whentlie piston is forced down, i.e., when the ven- 
tricle contracts, and the other, i.e., the arterial, valve 
opens. The diagrams on the preceding page illustrate this 
very well. 

During auricular contraction, the force of the blood pro- 
pelled into the ventricle is transmitted in all directions, but 
being insufficient to raise the semilunar valves, it is ex- 
pended in distending the ventricle, and in raising and 
gradually closing the auriculo-ventricular valves, which, 
when the ventricle is full, form a complete septum between 
it and the auricle. This elevation of the auriculo-ventricular 
valves is, no doubt, materially aided by the action of the 
elastic tissue which Dr. Markham has shown to exist so 
Isirgely in their structure, especially on the auricular sur- 
face. When the ventricle contracts, the edges of the valves 
are maintained in apposition by the simultaneous contrac- 
tion of the musculi pajnllares, which are enabled thus to act 
hy the arrangement of their tendinous cords just men- 
tioned. In this position the segments of the valves are 
held secure, even though the form and size of the orifice 
and the ventricle may change during the continued con- 
traction ; for the border pieces are held by their mutual 
apposition and the equal pressure of the blood on their 
ventricular surfaces ; and the middle pieces are secure by 
their 'great strength, and by the attachment of the ten- 
•dinous cords along their margins, these cords being always 
held tight by the contraction of the musculi papillares. A 
peculiar advantage, derived from the projection of these 
columns into the cavity of the ventricle, seems to be, that 
they prevent the valve from being converted into the aui'icle ; 
for, when the ventricle contracts, and the parts of its walls 
to which, through the medium of the columns, the ten- 
■dinous cords are affixed, approach the auriculo-ventricular 
orifices, there would be a tendency to slackness of the 
cords, and the valves might be everted, if it were not that 
while the wall of the ventricle is drawn towards the orifice, 



FUNCTION OF THE VALVES. [ 1 5 

the end of the simultaneously contracting fleshy column is 
drawn away from it, and the cords are held tight. 

What has been said applies equally to the auriculo- 
ventricular valves on both sides of the heart, and of both 
alike the closure is generally complete every time the 
ventricles contract. But in some circumstances, the closure 
of the tr icuspid-valve is not complete, and a certain 
quantity of blood is forced back into the auricle : and, 
since this may be advantageous, by preventing the over- 
filling of the vessels of the lungs, it has been called the 
safety-valve action of this valve (Hunter, Williinson King). 
The circumstances in which it usually happens are those in 
which the vessels of the lung are already full enough wheui 
the right ventricle contracts, as e.g., in certain pulmonary; 
diseases, in very active exertion, and in great efforts. In 
these cases, perhaps, because the right ventricle cannot 
contract quickly or completely enough, the tricuspid valve 
does not completely close, and the regurgitation of blood 
may be indicated by a pulsation in the jugular veins syn- 
chronous with that in the carotid arteries. 

The arterial or semilunar valves are, as already said, 
brought into action by the pressure of the arterial blood 
forced back towards the ventricles, when the elastic walls 
of the arteries recoil after being dilated by the blood pro- 
pelled into them in the previous contraction of the ventricle. 
The dilatation of the arteries is, in a peculiar manner, 
adapted to bring the valves into action. The lower borders 
of the semilunar valves are attached to the inner surface of 
a tendinous ring, which is, as it were, inlaid, at the orifice 
of the artery, between the muscular fibres of the ventricle 
and the elastic fibres of the walls of the artery. The tissue 
of this ring is tough, does not admit of extension under 
such pressure as it is commonly exposed to ; the valves are 
equally inextensile, being, as already mentioned, formed 
of tough, close-textured, fibrous tissue, with strong inter- 
woven cords, and covered with endocardium. Hence, when 

I 2 



Il6 THE CIRCULATIOX. 

the ventricle propels blood througli the orifice and into the 
canal of the artery, the lateral pressure which it exercises 
is sufficient to dilate the walls of the artery, but not 
enough to stretch in an equal degree, if at all, the unyield- 
ing valves and the ring to which their lower borders are 
attached. The effect, therefore, of each such propulsion 
of blood from the ventricle is, that the wall of the first 
portion of the artery is dilated into three pouches behind 
the valves, while the free margins of the valves, which had 
previously lain in contact with the inner surface of the 
artery (as at a, fig. 37), are drawn inward towards its 

Fig. 37.* 




centre (fig. 37, 33). Their positions may be explained by 
the foregoing diagrams, in which the continuous lines 
represent a transverse section of the arterial walls, the 
dotted ones the edges of the valves, firstly, when the valves 
are in contact with the walls (a), and, secondly, when the 
walls being dilated, the valves are drawn away from 
them (b). 

This position of the vialves and arterial walls is retained 
so long as the ventricle continues in contraction : but, so. 



* Fig. 37. Sections of aorta, to show the action of the semilunar 
valves. A is intended to show the valves, represented by the dotted 
lines, in contact with the arterial walls, represented by the continuous 
outer line, b (after Hunter) shows the arterial wall distended into 
three pouches (re), and drawn away from the valves which are straight- 
ened into the form of equilateral triangle, as represented by the dotted 
lines. 



FUNCTION OF THE VALVES. 



117 



soon as it relaxes, and the dilated arterial walls can recoil 
by their elasticity, they press the blood as well towards the 
ventricles as onwards in the course of the circulation. Part 
of the blood thus pressed back lies in the pouches («, fig. 
37, b) between the valves and the arterial walls ; and the 
valves are by it pressed together till their thin lunated 
margins meet in three lines radiating from the centre to 
the circumference of the artery (7 and 8, fig. 38). 

Pig. 38.* 




* Fig. 38. View of the base of tlie ventricular part of the heart, 
showing the relative position of the arterial and auriculo-ventricular 
orifices. — |. The muscular fibres of the ventricles are exposed by the 
removal of the pericardium, fat, blood-vessels, etc. ; the pulmonary 
artery and aorta have been removed by a section made immediately 
beyond the attachment of the semilunar valves, and the auricles have 
been removed immediately above the auriculo-ventricular orifices. The 
semilunar and auriculo-ventricular valves are in the nearly closed con- 
dition. I, I, the base of the right ventricle ; i', the conns arteriosus ; 
2, 2, the base of the left ventricle ; 3, 3, the divided wall of the right 
auricle ; 4, that of the left ; 5, 5', 5", the tricusi)id valve ; 6, 6', the 
mitral valve. In the angles between these segments are seen the 
smaller fringes frequently observed ; 7, the anterior part of the pul- 
monary artery ; 8, placed upon the posterior part of the root of the 
aorta ; 9, the right, 9', the left coronary artery. (From Quain's 
Anatomy. ) 



ii8 



THE CIRCULATION 



Fig- 39' 




Mr. Savory has clearly shown that this pressure of the 
blood is not entirely sustained by the valves alone, but in 
part by the muscular substance of the ventricle. Availing 
himself of a method of dissection 
hitherto apparently overlooked, 
namely, that of making vertical 
sections (fig. 39) through various 
parts of the tendinous rings, he 
has been enabled to show clearly 
that the aorta and pulmonary 
artery, expanding towards their 
- 3 termination, are situated upon the 
outer edge of the thick upper border 
of the ventricles, and that conse- 
quently the portion of each semi- 
lunar valve adjacent to the vessel 
passes over and rests upon the muscular substance — being 
thus supported, as it w^ere, on a kind of muscular floor 
formed by the free border of the ventricle. The result of 
this arrangement will be that the reflux of the blood will 
be most efficiently sustained by the ventricular walLf 

The eff'ect of the blood's pressure on the valve is, as said, 
to cause their margins to meet in three lines radiating from 
the centre to the circumference (7 and 8, fig. 38). The con- 
tact of the valve in this position, and the complete closure 
of the arterial orifice, are secured by the peculiar construc- 
tion of their borders before mentioned. Among the cords 
which are interwoven in the substance of the valves, are 
two of greater strength and prominence than the rest ; of 
which one extends along the free border of each valve, and 



* Fig, 39, Vertical section through the aorta at its junction with 
the left ventricle, i. Section of arterial coat. 2, Section of valve. 
3. Section of ventricle, 

t Mr, Savory's preparations, illustrating this and other points in 
relation to the structure and functions of the valves of the heart, are in 
the museum of St, Bartholomew's Hospital. 



SOUNDS OF THE HEART. 



119 



the other forms a double curve or festoon just below the 
free border. Each of these cords is attached by its outer 
extremities to the outer end of the free margin of its valve, 
and in the middle to the corpus Arantii ; they thus enclose 
a lunated space from a line to a line and a half in width, 
in which space the substance of the valve is much thinner 
and more pliant than elsewhere. When the valves are 
pressed down, all these parts or spaces of their surfaces 
come into contact, and the closure of the arterial orifice is 
thus secured by the apposition not of the mere edges of the 
valves, but of all those thin lunated parts of each, which 
lie between the free edges and the cords next below them. 
These parts are firmly pressed together, and the greater 
the pressure that falls on them, the closer and more secure 
is their apposition. The corpora Arantii meet at the centre 
of the arterial orifice when the valves are down, and they 
probably assist in the closure ; but they are not essential 
to it, for, not unfrequently, they are wanting in the valves 
of the pulmonary artery, which are then extended in larger, 
thin, flapping margins. In valves of this form, also, the 
inlaid cords are less distinct than in those with corpora 
Arantii ; yet the closure by contact of their surfaces is not 
less secure. 

Sounds of the Heart. 

When the ear is placed over the region of the heart, two 
sounds may be heard at every beat of the heart, which 
follow in quick succession, and are succeeded by a pause 
or period of silence. The first sound is dull and pro- 
longed ; its commencement coincides with the impulse of 
the heart, and just precedes the pulse at the wrist. The 
second is a shorter and sharper sound, with a somewhat 
flapping character, and follows close after the arterial pulse. 
The period of time occupied respectively by the two sounds 
taken together, and by the pause, are almost exactly equal. 



l2o THE CIRCULATION. 

The relative length of time occupied by each sound, as 
compared with the other, is a little uncertain. The difference 
may be best appreciated by considering the different forces 
concerned in the production of the two sounds. In one case 
there is a strong, comparatively slow, contraction of a 
large mass of muscular fibres, urging forward a certain 
quantity of fluid against considerable resistance ; while in 
the other it is a strong but shorter and sharper recoil of 
the elastic coat of the large arteries, — shorter because 
there is no resistance to the flapping back of the semilunar 
valves, as there was to their opening. The difference may 
be also expressed, as Dr. C. J. B. Williams has remarked, 
by saying the words lubb — dup. 

The events which correspond, in point of time, with the 
first sound, are the contraction of the ventricles, the first 
part of the dilatation of the auricles, the closure of the 
auriculo- ventricular valves, the opening of the semilunar 
valves, and the propulsion of blood into the arteries. The 
sound is succeeded, in about one-thirtieth of a second, by 
the pulsation of the facial artery, and in about one-sixth 
of a second, by the pulsation of the arteries at the wrist. 
The second sound, in point of time, immediately follows 
the cessation of the ventricular contraction, and corresponds 
with the closure of the semilunar valves, the continued 
dilatation of the auricles, the commencing dilatation of the 
ventricles, and the opening of the auriculo-ventricular 
valves. The pause immediately follows the second sound, 
and corresponds in its first part with the completed disten- 
sion of the auricles, and in its second with their contraction, 
and the distension of the ventricles, the auriculo-ventricular 
valves being all the time open, and the arterial valves 
closed. 

The chief cause of the first sound of the heart appears 
to be the vibration of the auriculo-ventricular valves, and 
also, but to a less extent, of the ventricular walls, and 
coats of the aorta and pulmonary artery, all of which parts 



SOUXDS OF THE HEART. 12 1 

are suddenly put into a state of tension at the moment of 
ventricular contraction. 

This view, long ago advanced by Dr. Billing, is sup- 
ported by the fact observed by Valentin, that if a portion 
of a horse's intestine, tied at one end, be moderately filled 
with water, without any admixture of air, and have a 
syringe containing water fitted to the other end, the first 
sound of the heart is exactly imitated by forcing in more 
water, and thus suddenly rendering the walls of the intes- 
tine more tense. 

The cause of the second sound is more simple than 
that of the first. It is probably due entirely to the 
sudden closure and consequent vibration of the semilunar 
valves when they are pressed down across the orifices of 
the aorta and pulmonary artery ; for, of the other events, 
which take place during the second sound, none is cal- 
culated to produce sound. The influence of the valves 
in producing the sound, is illustrated by the experiment 
already quoted from Valentin, and from others performed 
on large animals, such as calves, in which the results could 
be fully appreciated. In these experiments two delicate 
curved needles were inserted, one into the aorta, and another 
into the pulmonary artery, below the line of attachment of 
the semilunar valves, and, after being carried upwards 
about half an inch, were brought out again through the 
coats of the respective vessels, so that in each vessel one 
valve was included between the arterial walls and the wire. 
Upon applying the stethoscope to the vessels, after such 
an operation, the second sound had ceased to be audible. 
Disease of these valves, when so extensive as to interfere 
with their efficient action, also often demonstrates the same 
fact by modifying or destroying the distinctness of the 
second sound. 

One reason for the second sound being a clearer and 
sharper one than the first may be, that the semilunar 
valves are not covered in by the thick layer of fibres 



122 THE CIRCULATIOX. 

composing the walls of the heart to such an extent as are 
the auriculo -ventricular. It might be expected therefore 
that their vibration would be more easily heard through a 
stethoscope applied to the walls of the chest. 

The contraction of the auricles which takes place in the 
end of the pause is inaudible outside the chest, but may be 
heard, when the heart is exposed and the stethoscope 
■placed on it, as a slight sound preceding and continued 
into the louder sound of the ventricular contraction. 

The Impulse of the Heart. — At the commencement of 
each ventricular contraction, the heart may be felt to beat 
with a slight shock or impulse against the walls of the chest. 
This impulse is most evident in the space between the fifth 
and sixth ribs, between one and two inches to the left of 
the sternum. The force of the impulse, and the extent to 
which it may be perceived beyond this point, vary con- 
siderably in different individuals, and in the same indi- 
viduals under different circumstances. It is felt more 
distinctly, and over a larger extent of surface, in emaciated 
than in fat and robust persons, and more during a forced 
expiration than in a deep inspiration ; for, in the one case, 
the intervention of a thick layer of fat or muscle between 
the heart and the surface of the chest, and in the other the 
inflation of the portion of lung which overlaps the heart, 
prevents the impulse from being fully transmitted to the 
surface. An excited action of the heart, and especially a 
h}^ertrophied condition of the ventricles, will increase the 
impulse, while a depressed condition, or an atrophied state 
of the ventricular walls, will diminish it. 

The impulse of the heart is probably the result, in part, 
of a tilting forwards of the apex, so that it is made to 
strike against the waUs of the chest. This tilting move- 
ment is thought to be effected by the contraction of the 
spiral muscular fibres of the ventricles, and especially of 
certain of these fibres which, according to Dr. Reid, arise 
from the base of the ventricular septum, pass downwards 



IMPULSE OF THE IIEAET. 123 

and forwards, forming part of the septum, then emerge 
and curve spirally around the apex and adjacent portion 
of the heart. The whole extent of the movement thus 
produced is, however, but slight. The condition, which, 
no doubt, contributes most to the occurrence and character 
of the impulse of the heart, is its change of shape ; for, 
during the contraction of the ventricles, and the consequent 
approximation of the base towards the apex, the heart 
becomes more globular, and bulges so much, that a distinct 
impulse is felt when the finger is placed over the bulging 
portion, either at the front of the chest, or under the 
diaphragm. The production of the impulse is, perhaps, 
further assisted by the tendency of the aorta to straighten 
itself and diminish its curvature when distended with the 
blood impelled by the ventricle ; and by the elastic recoil 
of all the parts about the base of the heart, which, accord- 
ing to the experiments of Kurschner, are stretched down- 
ward and backward by the blood flowing into the auricles 
and ventricles during the dilatation of the latter, but re- 
cover themselves when, at the beginning of the contraction 
of the ventricles, the flow through the auriculo-ventricular 
orifices is stopped. But these last-mentioned conditions 
can only be accessory in the perfect state of things ; for the 
same tilting movement of the heart ensues when its apex 
is cut ofi", and when, therefore, no tension or change of 
form can be produced by the blood. 

Although what we generally recognise as the impulse of 
the heart is produced in the way just mentioned, the beat 
is not so simple a shock as it may seem when only felt 
by the finger. By means of an instrument called a cardio- 
graph, it may be shown to be compounded of three or four 
shocks, of which the finger can only feel the greatest. 

The cardiograph is a tube, dilated at one end into a 
cup or funnel, either open-mouthed or closed by an elastic 
membrane, while at the other it communicates with 
the interior of a small metal drum, one side of which is 



124 THE CIRCULATION. 

formed by an elastic membrane, on -vrbich rests a finely- 
balanced lever, like that of the sphygmograph (fig. 42). 

When used, the cup at one end of the tube is placed 
immediately over the part of the chest-wall at^ which the 
apex of the heart beats ; while the lever on the drum is 
placed in contact with a registering apparatus. (See de- 
scription of sphygmograph, p. 147.) When the heart 
beats, the shock communicates a series of impulses to the 
column of air in the now closed tube, with the effect ot 
raising the elastic wall of the drum, and of course the 
lever which is attached to it. A tracing of the heart's 
impulse is thus obtained in the same way as that of the 
pulse, in the arteries (figs. 44 and 45). 

The tracing shows that besides the strong beat which 
alone the finger recognises as the impulse of the heart, 
and which is caused by the contraction of the ventricles, 
there are other minor shocks which are imperceptible to 
the touch. The latter, M. iMarej^, by experiments on the 
lower animals, has proved to be the results, respectively, 
of the contraction of the auricles, and of the closure of the 
auriculo-ventricular and semilunar valves. 

Frequency and Force of the Hearths Action. 

The frequency with which the heart performs the actions 
we have described, may be counted by the pulses at the 
wrist, or in any other artery ; for these correspond with 
the contractions of the ventricles. 

The heart of a healthy adult man in the middle period 
of life, acts from seventy to seventy-five times in a minute. 
The frequency of the heart's action gradually diminishes 
from the commencement to near the end of life, but is said 
to rise again somewhat in extreme old age, thus : — 



ACTIOX OF THE HEART. 125 

In the embryo the average number of pulses in aniinnte is 150 

Just after birth from 140 to 130 

During the first year 130 to 115 

During the second year 115 to 100 

During the third year 100 to 90 

About tlie seventh year 90 to 85 

About the fourteenth year, the average number 

of pulses in a minute is from . . . 85 to 80 

In adult age . . . . . . . 80 to 70 

In old age 70 to 60 

In decrepitude 75 to 65 

In persons of sanguine temperament, the heart acts 
somewhat more frequently than in those of the phleg- 
matic ; and in the female sex more frequently than in the 
male. 

After a meal its action is accelerated, and still more so 
during bodily exertion or mental excitement ; it is slower 
during sleep. The effect of disease in producing temporary 
increase or diminution of the heart's action is well known. 
From the observation of several experimenters, it appears 
that, in the state of health, the pulse is most frequent in 
the morning, and becomes gradually slower as the day 
advances : and that this diminution of frequency is both 
more regular and more rapid in the evening than in the 
morning. It is found, also, that as a general rule, the 
pulse, especially in the adult male, is more frequent in the 
standing than in the sitting posture, and in the latter than 
in the recumbent position ; the difference being greatest 
between the standing and the sitting posture. The effect 
of change of posture is greater as the frequency of the 
pulse is greater, and, accordingly, is more marked in the 
morning than in the evening. Dr. Guy, by supporting 
the body in different postures, without the aid of muscular 
effort of the individual, has proved that the increased 
frequency of the pulse in the sitting and standing positions 
is dependent upon the muscular exertion engaged in main- 
taining them ; the usual effect of these postures on the 



126 THE CmCULATIOX. 

pulse being almost entirely prevented when the usually- 
attendant muscular exertion was rendered unnecessary. 
The effect of food, like that of change of posture, is greater 
in the morning than in the evening. According to Parrot, 
the frequency of the pulse increases in a corresponding 
ratio with the elevation above the sea ; and Dr. Frankland 
informed the author, that at the summit of Mont Blanc his 
pulse was about double the ordinary standard all the time 
he was there. After six hours' perfect rest and sleep at 
the top, it was 1 20, on descending to the corridor it fell to 
1 08, at the Grands Mulets it was S8, at Chamounix 56; 
normally, his pulse is 60. 

In health there is observed a nearly uniform relation 
between the frequency of the pulse and of the respirations; 
the proportion being, on an average, one of the latter to 
three or four of the former. The same relation is generally 
maintained in the cases in which the pulse is naturally 
accelerated, as after food or exercise ; but in disease this 
relation usually ceases to exist. In many affections accom- 
panied with increased frequency of the pulse, the respira- 
tion, is, indeed, also accelerated, yet the degree of its 
acceleration bears no definite proportion to the increased 
number of the heart's actions : and in many other cases, 
the pulse becomes more frequent without any accompany- 
ing increase in the number of respirations ; or, the respi- 
ration alone may be accelerated, the number of pulsations 
remaining stationary, or even falling below the ordinary 
standard. (On the whole of this subject the article Pulse 
by Dr. Guy, in the Cyclopaedia of Anatomy and Physiology, 
may be advantageously consulted.) 

The force with which the left ventricle of the heart con- 
tracts is about double that exerted by the contraction of 
the right : being equal (according to Valentin) to about 
3^th of the weight of the whole body, that of the right 
being equal only to —^ o^^ of the same. This difference 
in the amount of force exerted by the contraction of the two 



ACTIOX OF THE HEAllT. 127 

ventricles, results from tlie walls of the left ventricle being 
about twice as thick as those of the right. And the dif- 
ference is adapted to the greater degree of resistance which 
the left ventricle has to overcome, compared with that to 
be overcome by the right : the former having to propel 
blood through every part of the body, the latter only 
through the lungs. 

The force exercised by the auricles in their contraction 
has not been determined. Neither is it known with what 
amount of force either the auricles or the ventricles dilate ; 
but there is no evidence for the opinion, that in their dila- 
tation they can materially assist the circulation by any such 
action as that of a sucking-pump, or a caoutchouc bag, in 
drawing blood into their cavities. That the force which 
the ventricles exercise in dilatation is very slight, has been 
proved by Oesterreicher. He removed the heart of a frog 
from the body, and laid upon it a substance sufficiently 
heavy to press it flat, and yet so small as not to conceal the 
heart from view ; he then observed that during the con- 
traction of the heart, the weight was raised ; but that 
during its dilatation, the heart remained flat. And the 
same was shown by Dr. Clendinning, who, applying the 
points of a pair of spring callipers to the heart of a live 
ass, found that their points were separated as often as the 
heart swelled up in the contraction of the ventricles, but 
approached each other by the force of the spring when the 
ventricles dilated. Seeing how slight the force exerted in 
the dilatation of the ventricles is, it has been supposed 
that they are only dilated by the pressure of the blood 
impelled from the auricles ; but that both ventricles and 
auricles dilate spontaneously is proved by their continuing 
their successive contractions and dilatations when the heart 
is removed, or even when they are separated from one 
another, and when therefore no such force as the pressure 
of blood can be exercised to dilate them. By such spon- 
taneous dilatation they at least ofier no resistance to the 



128 THE CIRCULATIOX. 

influx of blood, and save the force -whicli would otherwise 
be required to dilate them. 

The capacity of the two ventricles is probably exactly the 
same. It is difficult to determine with certainty how much 
this may be ; but, taking the mean of various estimates, 
it may be inferred that each ventricle is able to contain on 
an average, about three ounces of blood, the whole of which 
is impelled into their respective arteries at each contraction. 
The capacity of the auricles is rather less than that of the 
ventricles : the thickness of their walls is considerably less. 
The latter condition is adapted to the small amount of 
force which the auricles require in order to empty them- 
selves into their adjoining ventricles; the former to the 
circumstance of the ventricles being partly filled with blood 
before the auricles contract. 

Cause of the Rhythmic Action of the Heart. 

It has been attempted in various ways to account for the 
existence and continuance of the rhythmic movements of 
the heart. By some it has been supposed that the contact 
of blood with the lining membrane of the cavities of the 
heart, furnishes a stimulus, in answer to which the walls 
of these cavities contract. But the fact that the heart, 
especially in Amphibia and fishes, will continue to contract 
and dilate regularly and in rhythmic order after it is 
removed from the body, completely emptied of blood, and 
even placed in a vacuum where it cannot receive the 
stimulus of the atmospheric air, is a proof that even if the 
contact of blood be the ordinary stimulus to the heart's 
contraction, it cannot alone be an explanation of its 
rhythmic motion. 

The influence of the mind, and of some afiections of the 
brain and spinal cord upon the action of the heart, proves 
that it is not altogether, or at all times, independent of 
the cerebro-spinal nervous system. Yet the numerous 
experiments instituted for the purpose of determining the 



RHYTHM OF THE HEART. 129 

exact relation in which, the heart stands towards this 
system, have failed to prove that the action is directly 
governed under ordinary circumstances by the power of 
any portion of the brain or spinal cord. Sudden destruc- 
tion of either the brain or spinal cord alone, or of both 
together, produces, immediately, a temporary interruption 
or cessation of the heart's action : but this appears to be 
only an effect of the sliock of so severe an injury; for, in 
some such cases, the movements of the heart are subse- 
quently resumed, and if artificial respiration be kept up, 
may continue for a considerable time ; and may then again 
be arrested by a violent shock applied through an injury 
of the stomach. While, therefore, we must admit an 
indirect or occasional influence exercised by, or through, 
the bi*ain and spinal cord upon the movements of the heart, 
and may believe this influence to be the greater the more 
highly the several organs are developed, yet it is clear that 
we cannot ascribe the regular determination and direction 
of the movements to these nervous centres. 

The persistence of the movements of the heart in their 
regular rhythmic order, after its removal from the body, 
and their capability of being then re-excited by an ordinary 
stimulus after they have ceased, proved that the cause of 
these movements must be resident within the heart itself. 
And it seems probable, fi:om the experiments and observa- 
tions of various observers, that it is connected with the 
existence of numerous minute ganglia of the sympathetic 
nervous system, which, with connecting nerve-fibres, are 
distributed through the substance of the heart. These 
ganglia appear to act as so many centres or organs for the 
production of motor impulses ; while the connecting nerve- 
fibres unite them into one system, and enable them to act 
in concert and direct their impulses so as to excite in 
regular series the successive contractions of the several 
muscles of the heart. The mode in which ganglia thus 
act as centres and co-ordinators of nervous power will be 



I30 THE CIRCULATION. 

described in the chapter on the Nervous System ; and 
it will appear probable that the chief peculiarity of the 
heart, in this respect, is due to the number of its ganglia, 
and the apparently equal power which they all exercise ; 
so that there is no one part of the heart whose action, more 
than another's, determines the actions of the rest. Thus, 
if the heart of a reptile be bisected, the rhythmic, suc- 
cessive actions of auricle and ventricle will go on in both 
halves : we therefore cannot say that the action of the 
right side determines or regulates that of the left, or vice 
versa ; and we must suppose that when they act together 
in the perfect heart, it is because they are both, as it were, 
set to the same time. Neither can we say that the auricles 
determine the action of the ventricles ; for, if they are 
separated, they will both contract and dilate in regular, 
though not necessarily similar, succession. A fact pointed 
out by Mr. Maiden shows how the several portions of each 
cavity are similarly adjusted to act alike, yet independently 
of each other. If a point of the surface of the ventricle 
of a turtle's or frog's heart be irritated, it will immediately 
contract, and very quickly afterwards all the rest of the 
ventricle will contract ; but, at the close of this general 
contraction, the part that was irritated and contracted first, 
is slightly distended or pouched out, showing that it was 
adjusted to contract in, and for only, a certain time, and 
that therefore as it began to contract first, so it began to 
dilate first. 

The best interpretation, perhaps, yet given of it, and 
of rhythmic processes in general, is that by Mr. Paget, 
who regards them as dependent on rhythmic nutrition, i.e.^ 
on a method of nutrition in which the acting parts are 
gradually raised, with time-regulated progress, to a certain 
state of instability of composition, which then issues in the 
discharge of their functions, ejj., of nerve-force in the case 
of the cardiac ganglia, by which force the muscular walls 
are excited to contraction. According to this view, there is 



EHYTHM OF THE HEART. 131 

in the nervous ganglia of the heart, and ia aU parts 
originating rhythmic processes, the same alternation of 
periods of action with periods of repose, during which the 
waste in the structure is repaired, as is observed in most 
of, if not all, the organic phenomena of life. All organic 
processes seem to be regulated with exact observance of 
time ; and rhythmic nutrition and action, as exhibited in 
the action of the heart, are but well-marked examples of 
such chronometric arrangement. 

We may conclude, then, that the nervous gangHa in 
the heart's substance are the immediate regulators of the 
heart's action, but that they are themselves liable to in- 
fluences, conveyed from without, through branches of the 
pneumogastric and sympathetic nerves. 

The pneum ogastricnervea^^are the media of an inhibitory I 
or restraining influence over the action of the heart ; for ' 
when by section their influence is withdrawn, the pulsa- 
tions^ of jthe organ are increased in frequency and strength ; 
while an opposite effect is produced by stimulating them, 
— the transmission of an electric current of even moderate 
strength, diminishing the pulsations, or stopping them 
altogether. Stimulation of the sympathetic nerves, on the 
other hand, accelerates and strengthens the heart's action. 

Various theories have been proposed to account for 
these peculiar results, but none of them are very satis- 
factory, and it is probable that many more facts must be 
discovered before any theory on the subject can be per- 
manently maintained. 

The connection of the action of the heart with the other 
organs, and the influences to which it is subject through 
them, are explicable from the connection of its nervous 
system with the other ganglia of the sympathetic, and with 
the brain and spinal cord through, chiefly, the pneumo- 
gastric nerves. But this influence is proved in a much 
more striking manner by the phenomena of disease than 
by any experimental or. other physiological observations. 

K 2 



132 THE CIRCULATIOX. 

The influence of a shock in arresting or modifying the 
action of the heart, — its very slow action after compression 
of the brain, or injury to the cervical portion of the spinal 
cord, — its irregidarities and palpitations in dyspepsia 
and hysteria, — are better evidence for the connection of 
the heart with the other organs through the nervous 
system, than are any results obtained by experiments. 

Effects of the Hearths Action. 

That the contractions of the heart supply alone a suffi- 
cient force for the circulation of the blood, appears to be 
established by the results of several experiments, of which 
the following is one of the most conclusive: — Dr. Sharpey 
injected bullock's blood into the thoracic aorta of a dog 
recently killed, after tying the abdominal aorta above the 
renal arteries, and found that, with a force just equal to 
that by which the ventricle commonly impels the blood in 
the dog, the blood which he injected into the aorta passed 
in a free stream out of the trunk of the vena cava inferior. 
It thus traversed both the systemic and hepatic capillaries ; 
and when the aorta was not tied above the renals, blood 
injected under the same pressure flowed freely through the 
vessels of the lower extremities. A pressure equal to that 
of one and a half or two inches of mercury was, in the 
same way, found sufficient to propel blood through the 
vessels of the lungs. 

But although it is probably true that the heart's action 
alone is sufficient to ensure the circulation, yet there exist 
several other forces which are, as it were, supplementary 
to the action of the heart, and assist it in maintaining the 
circulation. The principal of these supplemental forces 
have been already alluded to, and will now be more fully 
pointed out. 



STRUCTUEE OF AETEEIES. 



133 



THE AKTEHIES. 

The walls of tlie arteries are composed of three principal 
coats, termed the external or tunica adventitia, the middle, 
and the internal, while the latter is lined within by a single 
layer of tesselated epithelium. 

The external coat or tunica adventitia, the strongest and 
toughest part of the wall of the artery, is formed of areolar 
tissue, with which is mingled throughout a network of 
elastic fibres. At the inner part of this outer coat the 
elastic network forms in most arteries so distinct a layer 
as to be sometimes called the external elastic coat. 

The middle coat is composed of both muscular and elastic 
fibres. 

The former, which are of the pale or unstriped variety (see 
Chapter on Motion), are arranged 
for the most part transversely to 
the long axis of the artery; while 
the elastic element, taking also 
a transverse direction, is disposed 
in the form of closely inter- 
woven and branching fibres, 
which intersect in all parts the 
layers of muscular fibre. In 
arteries of various size there is 
a difference in the proportion of 
the muscular and elastic element, 
elastic tissue preponderating in 
the largest arteries, while this 
condition is reversed in those of medium and small size. 

The internal arterial coat is formed by layers of elastic 
tissue, consisting in part of coarse longitudinal branching 
fibres, and in part of a very thin and brittle membrane 
which possesses little elasticity, and is thrown into folds 




£. 



* Fig. 40. Muscular fibre-cells from human arteries, magnified 350 
diameters (Kolliker). a, natural state ; h, treated with acetic acid. 




134 THE CIRCULATIOX. 

or wrinkles when the artery contracts. This latter mem- 
brane, the striated or fenestrated coat of Ilenle, is pecu- 
liar in its tendency to curl up, when peeled off from the 
artery, and in the perforated and streaked appearance 
Fig. 41.* which it presents under 

the microscope. Its inner 
surface is lined with a de- 
licate layer of epithelium, 
composed of thin squamous 
elongated cells, which make 
it smooth and polished, and 
furnish a nearly imperme- 
able surface, along which 
the blood may flow with the 
smallest possible amount of 
resistance from friction. 
The walls of the arteries, with the possible exception of 
the epithelial lining and the layers of the internal coat 
immediately outside it, are not nourished by the blood 
which they convey, but are, like other parts of the body, 
supplied with little arteries, ending in capillaries and veins, 
which, branching throughout the external coat, extend for 
some distance into the middle, but do not reach the internal 
coat. These nutrient vessels are called vasa vasorum,' 
Nerve-fibres are also supplied to the walls of the arteries. 

The function of the arteries is to convey blood from, the 
heart to all parts of the body, and each tissue which enters 
into the construction of an artery has a special purpose to 
serve in this distribution. 

(l.) The external coat forms a strong and tough invest- 
ment, which, though capable of extension, appears princi- 
pally designed to strengthen the arteries ^and to guard 
against their excessive distension from the force of the 



* Fig. 41. Portion of fenestrated membrane from the crural artery, 
magnified 200 diameters, a, b, c, perforations (from Henle). 



STRUCTURE OF ARTERIES. 135 

heart's action. In it, too, tlie little vasa vasorum find a 
suitable tissue in which, to subdivide for the supply of the 
arterial coats. 

(2.) The purpose of the elastic tissue, which enters so 
largely into the formation of all the coats of the arteries, is^ 
1st, To guard the arteries from the suddenly exerted 
pressure to which they are subjected at each contraction of 
the ventricles. In every such contraction, the contents of 
the ventricles are forced into the arteries more quickly 
than they can be discharged into and through the capil- 
laries. The blood therefore being, for an instant, resisted 
in its onward course, a part of the force with which it was 
impelled is directed against the sides of the arteries ; under 
this force, which might burst a brittle tube, their elastic 
walls dilate, stretching enough to receive the blood, and 
as they stretch, becoming more tense and more resisting. 
Thus, by yielding, they, as it were, break the shock of the 
force impelling the blood, and exhaust it before they are 
in danger of bursting, through being overstretched. Elas- 
ticity is thus advantageous in all arteries, but chiefly so in 
the aorta and its large branches, which are provided, as 
already said, with a large proportional quantity of elastic 
tissue, in adaptation to the great force of the left ventricle, 
which falls first on them, and to the increased pressure of 
the arterial blood in violent expiratory efforts. 

On the subsidence of the pressure, when the ventricles 
cease contracting, the arteries are able, by the same elas- 
ticity, to resume their former calibre ; and in thus doing, 
they manifest the 2nd chief purpose of their elasticity, that, 
namely, of equalizing the current of the blood by main- 
taining pressure on the blood in the arteries during the 
periods at which the ventricles are at rest or dilating. If 
some such method as this had not been adopted — if for 
example the arteries had been rigid tubes, the blood, 
instead of flowing, as it does, in a constant stream, would 
have been propelled through the arterial system in a series 



136 THE CIRCULATIOX. 

of jerks corresponding to the ventricular contractions, witli 
intervals of almost complete rest during the inaction of the 
ventricles. But in the actual condition of the arteries, the 
force of the successive contractions of the ventricles is 
expended partly in the direct propulsion of the blood, and 
partly in the dilatation of the elastic arteries ; and in the 
intervals between the contractions of the ventricles, the 
force of the recoiling and contracting arteries is employed 
in continuing the same direct propulsion. Of course, the 
pressure exercised by the recoiling arteries is equally 
diffused in every direction through the blood, and th 
blood would tend to move backwards as well as onwards 
but that all movement backwards is prevented by the 
closure of the semi-lunar arterial valves, which takes place 
at the very commencement of the recoil of the arterial 
w^lls. 

By this exercise of the elasticity of the arteries, all the 
force of the ventricles is made advantageous to the circula- 
tion ; for that part of their force which is expended in 
dilating the arteries, is restored in full, according to that 
law of action of elastic bodies, by which they return to the 
state of rest with a force equal to that by which they were 
disturbed therefrom. There is thus no loss of force ; but 
neither is there any gain, for the elastic walls of the artery 
cannot originate any force for the propulsion of the blood — 
they only restore that which they received from the ventri- 
cles; they would not contract had they not first been 
dilated, any more than a spiral spring would shorten itself 
unless it were first elongated. The advantage of elasticity 
in this respect is, therefore, not that it increases, but that 
it equalizes or diffuses the force derived from the periodic 
contractions of the ventricles. The force with which the 
arteries are dilated every time the ventricles contract, 
might be said to be received by them in store, to be all 
given out again in the next succeeding period of dilatation 
of the ventricles. It is by this equalizing influence of the 



ELASTICITY OF ARTEEIES. 137 

successive branches of every artery that, at length, the 
intermittent accelerations produced in the arterial current 
by the action of the heart, cease to be observable, and the 
jetting stream is converted into the continuous and equable 
movement of the blood which we see in the capillaries and 
veins. 

In the production of a continuous stream of blood in the 
smaller arteries and capillaries, the resistance which is 
offered to the blood-stream in the capillaries (p. 161) is a 
necessary agent. Were there no greater obstacle to the 
escajye of blood from the arteries than exists to its entrance 
into them from the heart, the stream would be intermittent, 
notwithstanding the elasticity of the walls of the arteries. 

It is the resistance which the left ventricle meets with 
in forcing blood into the arteries that causes part of the 
force of its contraction to be expended in dilating them, 
or, as before remarked, in laying up in them a power 
which will act in the intervals of the ventricle's contrac- 
tion. 

(3.) By means of the elastic tissue in their walls (and of 
the muscular tissue also), the arteries are enabled to dilate 
and contract readily in correspondence with any temporary 
increase or diminution of the total quantity of blood in 
the body ; and within a certain range of diminution of 
the quantity, still to exercise due pressure on their 
contents. 

The elastic coat, however, not only assists in restoring 
the normal calibre of an artery after temporary dilatation, 
but also (4) may assist in restoring it after diminution of 
the calibre, whether this be caused by a temporary con- 
traction of the muscular coat, or the application of a com- 
pressing force from without. This action of the elastic 
tissue in arteries, is well shown in arteries which contract 
after death, but regain their average patency on the cessa- 
tion of post-mortem rigidity (p. 140). (5.) By means of 
their elastic coat the arteries are enabled to adapt them- 



138 THE CIKCULATIOX. 

selves to the different movements of the several parts of 
the body. 

We have already referred to the fact that the middle 
coat of the arteries is composed of unstriped muscular 
fibres, mingled with fine elastic filaments. The evidence 
for the muscular contractility of arteries may, however, be 
given briefly for the sake of the physiological facts on 
which it hinges. 

(i.) A\Tien a small artery in the living subject is exposed 
to the air or cold, it gradually but manifestly contracts. 
Hunter observed that the posterior tibial artery of a dog, 
when laid bare, became in a short time so much contracted 
as almost to prevent the transmission of blood ; and the 
observation has been often and variously confirmed. 
Simple elasticity could not effect this; for after death, 
when the vital muscular power has ceased, and the 
mechanical elastic one alone operates, the contracted 
artery dilates again. 

(2.) When an artery is cut across, its divided ends con- 
tract, and the orifices may be completely closed. The 
rapidity and completeness of this contraction vary in 
different animals; they are generally greater in young 
than in old animals ; and less, apparently, in man than in 
animals. In part this contraction is due to elasticity, but 
in part, no doubt, to muscular action ; for it is generally 
increased by the application of cold, or of any simple 
stimulating substances, or by mechanically irritating the 
cut ends of the artery, as by picking or twisting them. 
Such irritation would not be followed by these effects, if 
the arteries had no other power of contracting than that 
depending upon elasticity. 

(3.) The contractile property of arteries continues many 
hours after death, and thus affords an opportunity of dis- 
tinguishing it from elasticity. When a portion of an artery, 
the splenic, for example, of a recently killed animal, is 
exposed, it gradually contracts, and its canal may be 



MUSCULAEITY~OF ARTERIES. ' 139 

tlius completely closed : in this contracted state it remains 
for a time, varying from a few hours to two days : then it 
dilates again, and permanently retains the same size. If, 
while contracted, the artery be forcibly distended, its con- 
tractility is destroyed, and it holds a middle or natural size. 

This persistence of the contractile property after death 
was well shown in an observation of Hunter, which may 
be mentioned as proving, also, the greater degree of 
contractility possessed by the smaller than by the larger 
arteries. Having injected the uterus of a cow, which had 
been removed from the animal upwards of twenty-four 
hours, he found, after the lapse of another day, that the 
larger vessels had become much more turgid than when he 
injected them, and that the smaller arteries had contracted 
so as to force the injection back into the larger ones. 

The results of an experiment which Hunter made with 
the vessels of an umbilical cord prove still more strikingly 
the long continuance of the contractile power of arteries 
after death. In a woman delivered on a Thursday after- 
noon, the umbilical cord was separated from the foetus, 
having been first tied in two places, and then cut between, 
so that the blood contained in the cord and placenta was 
confined in them. On the following morning. Hunter tied 
a string round the cord, about an inch below the other 
ligature, that the blood might still be confined in the 
placenta and remaining cord. Having cut off this piece, 
and allowed all the blood to escape from its vessels, he 
attentively observed to what size the ends of the cut arte- 
ries were brought by the elasticity of their coats, and then 
laid aside the piece of cord to see the influence of the 
contractile power of its vessels. On Saturday morning, 
the day after, the mouths of the arteries were completely 
closed up. He repeated the experiment the same day with 
another portion of the same cord, and on the following 
morning found the results to be precisely similar. On the 
Sunday he performed the experiment the third time, but 



I40 ' THE CIRCULATIOX. 

the artery then seemed to have lost its contractility, for on 
the Monday morning, the mouths of the cut arteries were 
found open. In each of these experiments there was but 
little alteration perceived in the orifices of the veins. 

(4.) The influence of cold in increasing the contraction of 
a divided artery has heen referred to : it has been shown, 
also, by Schwann, in an experiment on the mesentery of a 
living toad. Having extended the mesenter under the 
microscope, he placed upon it a few drops of water, the 
temperature of which was some degrees lower than that of 
the atmosphere. The contraction of the vessels soon com- 
menced, and gradually increased until, at the expiration of 
ten or fifteen minutes, the diameter of the canal of an 
artery, which at first was 0*0724 of an English line, was 
reduced to 0"0276. The arteries then dilated again, and 
at the expiration of half an hour had acquired nearly their 
original size. By renewing the application of the water, 
the contraction was reproduced : in this way the experi- 
ment could be performed several times on the same artery. 
It is thus proved, that cold will excite contraction in the 
walls of very small, as well as of comparatively large 
arteries : it could not produce such contraction in a merety 
elastic substance ; but it is a stimulus to the organic mus- 
cular fibres in many other parts, as well as in the arterial 
coat ; as, e.g., in the skin, the dartos, and the walls of the 
bronchi. 

(5.) Lastly, satisfactory evidence of the muscularity of 
the arterial coats is furnished by the experiments of Ed. 
and E. H. Weber, and of Professor Kolliker, in which 
they applied the stimulus of electro-magnetism to small 
arteries. The experiments of the Webers were performed 
on the small mesenteric arteries of frogs j and the most 
striking results were obtained when the diameter of the 
vessels examined did not exceed from 4- to — of a Paris 
line. When a vessel of this size was exposed to the elec- 
tric current, its diameter in from five to ten seconds, became 



FUNCTIONS OF MUSCULAR COAT. 141 

one-third less, and the area of its section about one-half. 
On continuing the stimulus, the narrowing gradually in- 
creased, until the calibre of the tube became from three to 
six times smaller than it was at first, so that onty a single 
row of blood -corpuscles could pass along it at once ; and 
eventually the vessel was closed and the current of blood 
arrested. 

With regard to the purpose served by the muscular coat of 
the arteries, there appears no sufficient reason for supposing 
that it assists, to more than a very small degree, in pro- 
pelling the onward current of blood. Its most important 
office is that of regulating the quantity of blood to be 
received by each part, and of adjusting it to the require- 
ments of each, according to various circumstances, but 
chiefly and most naturally, according to the activity with 
w^hich the functions of each part are at different times per- 
formed. The amount of work done by each organ of the 
body varies at different times, and the variations often 
quickly succeed each other, so tliat, as in the brain for 
example, during sleep and waking, within the same hour 
a part may be now very active and then inactive. In all 
its active exercise of function, such a part requires a larger 
supply of blood than is sufficient for it during the times 
when it is comparatively inactive. It is evident that the 
heart cannot regulate the supply to each part at different 
periods, neither could this be regulated by any general 
and uniform contraction of the arteries ; but it may be 
regulated by the power which the arteries of each part 
have, in their muscular tissue, of contracting so as to 
diminish, and of passively dilating or yielding so as to 
permit an increase of, the supply of blood, according as 
the requirements of the part may demand. And thus, 
while the ventricles of the heart determine the total 
quantity of blood, to be sent onwards at each contraction, 
and the force of its propulsion, and while the large and 
merely elastic arteries distribute it and equalise its stream. 



142 THE CIECULATIOX. 

the smaller arteries with muscular tissue add to these tvi^o 
purposes, that of regulating and determining, according to 
its requirements, the proportion of the whole quantity of 
blood which shall be distributed to each part. 

It must be remembered, however, that this regulating 
function of the arteries is itself governed and directed by 
the nervous system. 

The muscular tissue of arteries is supplied with nerves 
chiefly, if not entirely, by branches from the sympathetic 
system. These so-called vaso-motor nerves are again con- 
nected, through the medium of ganglia, with the fibres 
from the sympathetic system supplied to the organs 
nourished by these same arteries. Thus, any condition in 
these organs which causes them to need a different amount 
of blood, whether more or less, produces a certain im- 
pression on their nerves, and by these the impression is 
carried to the ganglia, and thence reflected along the 
nerves which supply the arteries. The muscular element 
of these vessels responds in obedience to the impression 
conveyed to it by the nerves ; and, according to its contrac- 
tion or dilatation, is a larger or smaller quantity of blood 
allowed to pass. 

Another function of the muscular element of the middle 
coat of arteries is, doubtless, to co-operate with the elastic 
in adapting the calibre of the vessels to the quantity of 
blood which they contain. For the amount of fluid in the 
blood-vessels varies very considerably even from hour to 
hour, and can never be quite constant, and were the elastic 
tissue only present, the pressure exercised by the waUs of 
the containing vessels on the contained blood would be 
sometimes very small, and sometimes inordinately great. 
The presence of a muscular element, however, provides 
for a certain uniformity in the amount of pressure exer- 
cised ; and it is by this adaptive, uniform, gentle, muscular, 
contraction, that the tone of the blood-vessels is maintained. 
Deficiency of this tone is the cause of the soft and yield- 



THE PULSE. 



143 



ing pulse, and its unnatural excess of the hard and tense 
one. 

The elastic and muscular contraction of an artery may 
also be regarded as fulfilling a natural purpose when, the 
artery being cut, it first limits and then, in conjunction 
with the coagulated fibrin, arrests the escape of blood. It 
is only in consequence of such contraction and coagulation 
that we are free from danger through even very slight 
wounds ; for it is only when the artery is closed that the 
processes for the more permanent and secure prevention of 
bleeding are established. 

Mr. Savory has shown that the natural state of all arte- 
ries, in regard at least to their length, is one of tension — 
that they are always more or less stretched, and ever ready 
to recoil by virtue of their elasticity, whenever the oppos- 
ing force is removed. The extent to which the divided 
extremities of arteries retract is a measure of this tension, 
not of their elasticity. 

From what has been said in the preceding pages, it 
appears that the office of the arteries in the circulation is, — 
1st, the conveyance and distribution of blood to the several 
parts of the body ; 2nd, the equalization of the current, and 
the conversion of the pulsatile jetting movement given to- 
the blood by the ventricles, into an uniform flow ; ;^rd, the 
regulation of the supply of blood to each part, in accord- 
ance with its demands. 

The Pulse. 

The jetting movement of the blood, which, as just stated, 
it is one of the offices of the arteries to change into an uni- 
form motion, is the cause of the pulse, and therefore needs 
a separate consideration. \Ye have already said, that as the 
blood is not able to pass through the arteries so quickly as 
it is forced into them by the ventricle, on account of the 
resistance it experiences in the capillaries, a part of the 



144 THE CIRCULATIOX. 

force with which, the heart impels the blood is exercised 
upon the walls of the vessels which it distends. The 
distension of each artery increases both its length and its 
diameter. In their elongation, the arteries change their 
form, the straight ones becoming curved, or having such a 
tendency, and those already curved becoming more so ; •*• 
but they recover their previous form as well as their dia- 
meter when the ventricular contraction ceases, and their 
elastic walls recoil. The increase of their curves which 
accompanies the distension of arteries, and the succeeding 
recoil, may be well seen in the prominent temporal artery 
of an old person. The elongation of the artery is in such 
a case quite manifest. 

The dilatation or increase of the diameter of the artery 
is less evident. In several reptiles, it may be seen without 
aid, in the immediate vicinity of the heart, and it may be 
watched, with a simple magnifying glass, in the aorta of 
the tadpole. Its slight amount in the smaller arteries, the 
difficulty of observing it in opaque parts, and the rapidity 
with which it takes place, are sufficient to account for its 
being, in Mammalia, imperceptible to the eye. But in 
these also experiment has proved its occurrence. Flourens, 
in evidence of such dilatation, says he encircled a large 
artery with a thin elastic metallic ring cleft at one point, 
and that at the moment of pulsation the cleft part became 
jDerceptibly widened. 

This dilatation of an artery, and the elongation producing 
curvature, or increasing the natural curves, are sensible to 
the finger placed over the vessel, and produce the pulse. 
The mind cannot distinguish the sensation produced by 
the dilatation from that produced by the elongation and 



* There is, perhaps, an exception to tliis in the case of the aorta, of 
which the curve is by some supposed to be diminished when it is elon- 
gated ; but if this be so, it is because only one end of the arch is im- 
moveable ; the other end, with the heart, may move forward slightly 
when the ventricles contract. 



THE PULSE. 



145 



curving ; tliat whicli it perceives most plainly, however, is 
the dilatation.* 

The pulse — due to any given beat of the heart — is not 
perceptible at the same moment in all the arteries of the 
body. Thus it can be felt in the carotid a very short time 
before it is perceptible in the radial artery, and in this 
vessel again before the dorsal artery of the foot. The 
delay in the beat is in proportion to the distance of the 
artery from the heart, but the difference in time between 



* For this fact, which, is contrary to the commonly accepted doctrine, 
I am indebted to my friend, Dr. Hensley, who has kindly furnished me 
with the following note on the subject : — 

By determining the conditions of equilibrium of a portion of artery 
-supposed cylindrical and filled with blood at a given pressure, it is easily 
shown that the transverse tension is double the longitudinal. 

Also it may be shown experimentally that, if strips of equal breadth, 
cut in the two directions from one of the larger arteries, be stretched by 
equal weights, the stretching of the transverse slip is somewhat greater 
than that of the longitudinal one. 

(^By the word stretching is to be understood amount of stretching, and 
not increase of length: — it may be measured by the ratio ichich the 
increase of length bears to the original length: — Thus things whose 
natioral lengths are 5 and 10 inches are equally stretched when tlieir 
lengths are made 6 and 12 inches respectively.) 

Such experiments also show that, within certain limits, the stretching 
of each strip varies directly as its tension. 

Hence it avlU be seen that the transverse stretching of an artery, when 
iilled with blood, must be somewhat more than double its longitudinal 
stretching. 

This being true for different blood pressures, the difference between 
the transverse stretchings for different pressures must be somewhat more 
than double the difference between the corresponding longitudinal 
stretchings ; and thus we can hardly be justified in saying that the 
increase of longitudinal stretching which takes place with the pulse is 
greater than the increase of transverse stretching. 

It must also be remembered that the arteries are, under all circum- 
stances, naturally in a state of tension longitudinally, and that their 
length, therefore, cannot be increased at all until the blood pressure is 
increased beyond a certain point— (Ed.) 



146 



THE CIRCULATION. 



the beat of any two arteries never exceeds probably J to |- 
of a second. 

A great deal of light has been thrown on what may 
be called the form of the pulse by the sphygmograph (figs. 
42 and 43). The principle on which the sphygmograph 
acts is very simple (see fig. 42). The small button re- 
places the finger in the ordinary act of taking the pulse, 
and is made to rest lightly on the artery, the pulsations of 
which it is desired to investigate. The up-and-down 
movement of the button is communicated to the lever, to 
the hinder end of which is attached a slight spring, which 
allows the lever to move up, at the same time that it is 



Fig. 42. 



=^ 



Fi(j. 43-t 




just strong enough to resist its making any sudden jerk, 
and in the interval of the beats also to assist in bringing it 



* Fig. 42. Diagram of the mode of action of the Sphygmograph. 
f Fig. 43. The Sphygmograph applied to the arm. 



PULSE-THACINGS. 



147 



back to its original position. For ordinary purposes, the 
instrument is bound on the wrist (fig. 43). 

It is evident that the beating of the pulse with the 
reaction of the spring will cause an up-and-down move- 
ment of the lever, and if the extremity of the latter be 
inked, it will write the effect on the card, which is made 
to move by clockwork in the direction of the arrow. Thu^ 
a tracing of the pulse is obtained, and in this way much 
more delicate effects can be seen, than can be felt on the 
application of the finger. 

Fig. 44 represents a healthy pulse-tracing of the radial 
artery, but somewhat deficient in tone. On examination, 
we see that the up-stroke which represents the beat of the 
pulse is a nearly vertical line, while the down-stroke is 

Fiff. 44.* 



Fifj. 45. t 



Fuj. 46. J 




very biauting, and interrupted by a slight re-ascent. The 
more vigorous the pulse, if it be healthy, the less is this 
re-ascent, and vice versa. Fig. 45 represents the tracing 



* Fig. 44. Pulse-tracing of radial arterj^ somewhat deficient in tone. 
t Fig. 45. Finn and long pulse of vigorous health. 
+ Fig. 46. Pulse-tracing of radial artery, with double apex. 
The above tracings are taken from Dr. Sanderson's work " On the 
Sphygmograph. " 

L 2 



148 THE CIRCULATION. 

of a healthy pulse in which the tone of the vessel is better 
than in the last instance, and the down-stroke is therefore 
less interrupted. 

Sometimes the up-stroke has a double apex, as in fig. 
46. This will be explained hereafter. 

Before proceeding to consider the formation of the pulse, 
as shown by these tracings, it is necessary to consider what 
are the elements combined to produce it. 

The heart at regular intervals discharges a certain 
quantity of blood into the arteries and their branches, 
already filled, though not distended to the utmost, with 
fluid. This fresh quantity of blood obtains entrance by 
the yielding of the artery's elastic walls, and, on the 
cessation of the propelling force, and when these walls 
recoil, the blood is prevented from returning into the 
ventricle whence it is issued, by the shutting of the semi- 
lunar valves in the manner before described (p. 1 1 7). The 
pressure, therefore, which is exercised on the blood by the 
contracting arterial walls, will cause it to travel in a direc- 
tion away from the heart, or, in other words, towards the 
capillaries and veins. 

It was formerly supposed that the pulse was caused not 
by the direct action of the ventricle, but by the propaga- 
tion of a wave in consequence of the elastic recoil of the 
large arteries, after their distension ; and successive acts of 
dilatation and recoil, extending along the arteries in the 
direction of the circulation, were supposed to account for 
the later appearance of the pulse in the vessels most 
distant from the heart. The fact, however, that the pulse 
is perceptible in every part of the arterial system previous 
to the occurrence of the second sound of the heart, that is, 
previous to the closure of the aortic valves, is a fatal 
objection to this theory. For, if the pulse were the effect 
of a wave propagated by the alternate dilatation and con- 
traction of successive portions of the arterial tube, it ought, 
in all the arteries except those nearest to the heart, to 



PULSE-TRACIXGS. 



149 



follow or coincide with, but could never precede, the second 
sound of the heart ; for the first effect of the elastic recoil 
of the arteries first dilated is the closure of the aortic 
valves ; and their closure produces the second sound. 

The theory which seems to reconcile all the facts of the 
case, and especially those two which appear most opposed, 
namely, th^t the -pulse always precedes the second sound 
of the heart, and yet is later in the arteries far from the 
heart than in those near it, may be thus stated : — It sup- 
poses that the blood which is impelled onwards by the left 
ventricle does not so impart its pressure to that which the 
arteries already contain, as to dilate the whole arterial 
system at once ; but that it enters the arteries, it displaces 
and propels that which they before contained, and flows on 
with what may be called a head-wave, like that which is 
formed when a rapid stream of water overtakes another 
moving more slowly. The slower stream off'ers resistance 
to the more rapid one, till their velocities are equalized : 
and, because of such resistance, some of the force of the 
more rapid stream of blood just expelled from the ventricle, 
is diverted laterally, and with the rising of the wave the 
arteries nearest the heart are dilated and elongated. They 
do not at once recoil, but continue to be distended so long 
as blood is entering them from the ventricle. The wave 
at the head of the more rapid stream of blood runs on, 
propelled and maintained in its velocity by the continuous 
contraction of the ventricle : and it thus dilates in succes- 
sion every portion of the arterial system, and produces the 
pulse in all. At length, the whole arterial system (where- 
in a pulse can be felt) is dilated ; and at this time, when 
the wave we have supposed has reached all the smaller 
arteries, the entire system may be said to be simulta- 
neously dilated ; then it begins to contract, and the con- 
tractions of its several parts ensue in the same succession 
as the dilatations, commencing at the heart. The contrac- 
tion of the first portion produces the closure of the valves 



ISO THE CIRCULATIOX. 

and the second sound of the heart ; and both it and the 
progressive contractions of all the more distant parts main- 
tain, as already said, that pressure on the blood during 
the inaction of the ventricle, by which the stream of the 
arterial blood is sustained between the jets, and is finally 
equalized by the time it reaches the capillaries. 

It may seem an objection to this theory, that it would 
probably require a larger quantity of blood to dilate all 
the arteries than can be discharged by the ventricle at each 
contraction. But the quantity necessary for such a pur- 
pose is less than might be supposed. Injections of the 
arteries prove that, including all down to those of about 
one-eighth of a line in diameter, they do not contain on 
an average more than one and a half pints of fluid, even 
when distended. There can be no doubt, therefore* that 
the three or four ounces which the ventricle is supposed 
to discharge at each contraction, being added to that 
which already fills the arteries, would be sufiicient to 
distend them aU. 

A distinction must be carefully made between the passage 
of the wave along the arteries, and the velocity of the stream 
(p. 155) of blood. Both wave and current are present; but 
the rates at which they travel are very different, that of the 
wave being twenty or thirty times as great as that of the 
current. 

Returning now to the consideration of the pulse-tracings 
(p. 147), it may be remarked that, in each, the up-stroke 
corresponds with the period during which the ventricle is 
contracting; the down-stroke, with the interval between 
its contractions, or in other words with the recoil, after 
distension, of the elastic arteries. In the large arteries, 
when at least there is much loss of tone, the up-stroke is 
double, the almost instantaneous propagation of the force 
of contraction of the left ventricle along the column of 
blood in the arteries, or the percussion-impulse, as it 
is termed by Dr. Sanderson, being sufficiently strong to 



I 



PULSE-TEACIXGS. 1 5 1 

jerk up the lever for an instant, while the wave of blood, 
rather more slowly propagated from, the ventricle, catches 
it, so to speak, as it begins to fall, and again slightly 
raises it. 

In the radial artery tracings, on the other hand, we see 
that the up-stroke is single. In this case the percussion- 
impulse is not sufficiently strong to jerk up the lever and 
produce an effect distinct from that of the systolic wave 
which immediately follows it, and which continues and 
completes the distension. In cases of feeble arterial 
tension, however, the percussion-impulse may be traced 
by the sphygmograph, not only in the carotid pulse, but 
to a less extent in the radial also (fig. 46). 

In looking now at the down-stroke (fig. 44) in the 
tracings, we see that in the case of an artery with defi- 
cient tone, it is interrupted by a well-marked notch, or, in 
other words, that the descent is interrupted by a slight 
uprising. There are indications also of slighter irregu- 
larities or vibrations during the fall of the lever ; while 
these are alone to be seen in the pulse of healthy or, in 
other words, when the walls of the artery are of good 
tone (fig. 45). In some cases of disease the re-ascent is 
so considerable as to be perceptible to the finger, and this 
double beat has received the technical name of "dicrotous'' 
pulse. As a diseased condition this has long been recog- 
nized, but it is only since the invention of the sphygmo- 
graph that it has been found to belong in a certain degree 
to the normal pulse also. 

Various theories have been framed to account for the 
dicrotism of the pulse. By some, it is supposed to be due 
to the aortic valves, the sudden closure of which stops the 
incipient regurgitation of blood into the ventricle, and 
causes a momentary rebound throughout the arterial 
system ; while Dr. Sanderson considers it to be caused by 
a kind of rebound from the periphery rather than from 
the central part of the circulating apparatus. 



152 



THE CIRCULATIOX. 



Force of the Blood in the Arteries, 

The force with which the ventricles act in their con- 
traction, and the reasons for believing it sufficient for the 
circulation of the blood, have been already mentioned. 
Both calculation and experiment have proved, that very- 
little of this force is consumed in the arteries. Dr. Thomas 
Fig. 47. Young calculated that the loss of 

force in overcoming friction and other 
hindrances in the arteries would be so 
slight, that if one tube were introduced 
into the aorta, and another into any 
other artery, even into one as fine as 
hair, the blood would rise in the tube 
from the small vessel to within two 
inches of the height to which it would 
rise from the large vessel. The cor- 
rectness of the calculation is esta- 
blished by the experiments of Poi- 
seuille, who invented an instrument 
named a hsemadynamometer, for es- 
timatiug the statical pressur^exer- 
cised by the blood upon the walls of 
the arteries. It consists of a long 
glass tube, bent so as to have a short 
horizontal portion (fig. 47), a branch 
(2) descending at right angles from it^ 
and a long ascending branch (3). 
Mercury poured into the ascending 
and descending portions, will necessarily have the same 
level in both branches, and in a vertical position the 
height of its column must be the same in both. If, now, 
the blood is made to flow from an artery, through the 
horizontal portion of the tube (which should contain a \ 
solution of carbonate of potash to prevent coagulation} I 
into the descending branch, it will exert on the mercury a 




" \it..-i- 



FOECE OF BLOOD IX AETEEIES. 1 55 

pressure equal to the force by which it is moved in the 
arteries ; and the mercury will, in consequence, descend in 
this branch, and ascend in the other. The depth to which 
it sinks in the one branch, added to the height to which it 
rises in the other, will give the whole height of the column 
of mercury which balances the pressure exerted by the 
blood ; the weight of the blood, which takes the place of 
the mercury in the descending branch, and which is more 
than ten times less than the same quantity of quicksilver, 
being subtracted. Poiseuille thus calculated the force 
with which the blood moves in an artery, according to the 
laws of hydrostatics, from the diameter of the artery, and 
the height of the column of quicksilver ; that is to say, 
from the weight of a column of mercury, whose base is a 
circle of the same diameter as the artery, and whose height 
is equal to the difference in the levels of the mercury in 
the two branches of the instrument. He found the blood's 
pressure equal in all the arteries examined ; difference in 
size, and distance from the heart being unattended by any 
corresponding difference of force in the circulation. The 
height of the column of mercury displaced by the blood 
was the same in all the arteries of the same animal. The 
correctness of these views having been questioned, Poi- 
seuille ha'S recently repeated his observations, and obtained 
the same results. 

From the mean result of several observations on horses 
and dogs, 4ie calculated that the force with which the 
blood is moved in any large artery, is capable of support- 
ing a column of mercury six inches and one and a half 
lines in height, or a column of water seven feet one line in 
height. With these results, the more recent observations 
of other experimenters closely accord. Poiseuille's experi- 
ments having thus shown to him that the force of the 
blood's motion is the same in the most different arteries, 
he concluded that, to measure the amount of the blood's 
pressure in any artery of which the calibre is known, it is 



154 THE CIECULATIOX. 

necessary merely to multiply the area of a transverse sec- 
tion of a vessel by the height of the column of mercury 
I j which is already known to be supported by the force of 
N^, \ the blood in any part of the arterial system. The weight 
', of a column of mercury of the dimensions thus found, will 
\ represent the pressure exerted by the column of blood. 
And assuming that the mean of the greatest and least 
height of the column of mercury found, by experiments 
on different animals, to be supported by the force of the 
blood in them, is equivalent to the height of the column 
which the force of the blood in the human aorta would 
support, he calculated that about 4 lbs. 4 oz. avoirdupois 
would indicate the static force with which the blood is 
impelled into the human aorta. By the same calculation, 
he estimated the force of the circulation in the aorta of the 
mare to be about 1 1 lbs. 9 oz. avoirdupois: and that in the 
radial artery at the human wrist only 4 drs. We have 
already seen that the muscular force of the right ventricle 
is equal to only one half that of the left, consequently, if 
Poiseuille's estimate of the latter be correct, the force with 
which the blood is propelled into the lungs will only be 
equal to 2 lbs. 2 oz. avoirdupois. 

The amounts above stated indicate the pressure exerted 
by the blood at the several parts of the arterial system at 
the time of the ventricular contraction. During the dila- 
tation, this pressure is somewhat diminished. Hales 
observed, that the column of blood in the ttlbe inserted 
into an artery, falls an inch, or rather more, after each 
pulse; Ludwig has observed the same, and recorded it 
more minutely. The pressure is also influenced by the 
various circumstances which affect the action of the heart ; 
the diminution or increase of the pressure being pro- 
portioned to the weaker or stronger action of this organ. 
Valentin observed that, on increasing the amount of 
' blood by the injection of a fresh quantity into it, the 
pressure in the vessels was also increased, while a 



VELOCITY OF BLOOD IN AETERIES. 155 

contrary effect ensued on diminishing the quantity of 
blood. 

Velocity of the Blood in the Arteries. 

The velocity of the stream of blood is greater in the 
arteries than in any other part of the circulatory system, 
and in them it is greatest in the neighbourhood of the 
heart, and during the ventricular systole; the rate of 
movement diminishing during the diastole of the ven- 
tricles, and in the parts of the arterial system most distant 
from the heart. From Volkmann's experiments with the 
haemodromometer, it may be concluded that the blood 
moves in the large arteries near the heart at the rate of 
about ten or twelve inches per se£ond. Vierordt calculated 
the rapidity of the stream at about the same rate in the 
arteries near the heart, and at two and a quarter inches 
per second in the arteries of the foot. 

THE CAPILLAKIES. 

In al^ organic textures, except some parts of the corpora , 
cavernosa of the penis, and of the uterine placenta, and of 
the spleen, the transmission of the blood from the minute 
branches of the arteries to the minute veins is effected 
through a network of microscopic vessels, in the meshes 
of which the proper substance of the tissue lies (fig. 48). 
This may be seen in all minutely injected preparations; 
and during life, by the aid of the microscope, in any trans- 
parent vascular parts, — such as the web of the frog's foot, 
the tail or external branchipc of the tadpole, or the wing 
of the bat. 

The ramifications of the minute arteries form repeated 
anastomoses with each other and give off the capillaries 
which, by their anastomoses, compose a continuous and 
uniform network, from which the venous radicles, on the 
other hand, take their rise. Tho reticulated vessels con- 
necting the arteries and veins are called capillary, on 



156 



THE CIRCULATIOX. 



account of their minute size ; and intermediate vessels, on 
account of their position. The point at which the arteries 

terminate and the minute veins 
commence, cannot be exactly de- 
fined, for the transition is gradual ; 
but the intermediate network has, 
nevertheless, this peculiarity, that 
the small vessels which compose 
it maintain the same diameter 
throughout; they do not dimmish 
in diameter in one direction, like 
arteries and veins ; and the 
meshes of the network that they 
compose are more uniform in 
shape and size than those formed 
by the anastomoses of the minute 
arteries and veins. 

The structure of the capillaries 
is much more simple than that of 
the arteries or veins. Their walls 
are composed of a single layer of elongated or radiate, 
flattened and nucleated cells, so joined and dovetailed 
together as to form a continuous transparent membrane 
(fig. 49). Outside these cells, in the larger capillaries, 
there is a structureless, or very finely fibrillated membrane, 
on the inner surface of which they are laid down. 

The diameter of the capillary vessels varies somewhat in 
the difi'erent textures of the body, the most common size 
being about -j-oVo-*^ ^^ ^^ inch. Among the smallest may 
be mentioned those of the brain, and of the follicles 
of the mucous membrane of the intestines ; among the 




* Fig. 48. Blood-vessels of an intestinal villus, representing the 
arrangement of capillaries between the ultimate venous and arterial 



branches ; a, a, the arteries ; b, the vein. 



THE CAPILLARIES. 



157 



largest, those of the skin, and especially those of the 
medulla of bones. 

The form of the capillary network presents considerable 
variety in the different textures of the body : the varieties 




consisting principally of modifications of two chief kinds 
of mesh, the rounded and the elongated. That kind in 
which the meshes or interspaces have a roundish form is 
the most common, and prevails in those parts in which the 
capillary network is most dense, such as the lungs (fig. 50), 



* Fig. 49. Magnified view of capillary vessels from the bladder of 
the cat. — A, V, an artery and a vein ; i, transitional vessel between 
them and c, c, the capillaries. The muscular coat of the larger vessels 
is left out in the figure to allow the epithelium to be seen : at c', a 
radiate epithelium scale with four pointed processes, running out upon 
the four adjoining capillaries (after Chrzonszczewesky, A^irch. Arch. 
1866). 



158 



THE CIRCULATIOX 



most glands, and mucous membranes, and the cutis. The 
meshes of this kind of network are not quite circular, 
but more or less angular, sometimes presenting a nearly 
regular quadrangular or polygonal form, but being more 
frequently irregular. The capillary network with elon- 
gated meshes (fig. 51) is observed in parts in which the 



Fig. 50.* 




Fig. Si.f 




vessels are arranged among bundles of fine tubes or fibres, 
as in muscles and nerves. In such parts, the meshes 
usually have the form of a parallelogram, the short sides of 
which may be from three to eight or ten times less than the 
long ones ; the long sides always corresponding to the axis 
of the fibre or tube, by which it is placed. The appearance 
of both the rounded and elongated meshes is much varied 
according as the vessels composing them have a straight 
or tortuous form. Sometimes the capillaries have a looped 



* Fig. 50. Network of capillary vessels of the air-cells of the horse's 
lung, magnified, a, a, capillaries proceeding from h, h, terminal 
"branches of the pulmonary artery (after Frey). 

f Fig. 51. Injected capillary vessels of muscle, seen with a low 
magnifying power (Sharpey). 



THE CAPILLAEIES. 



159 



arrangement, a single capillary projecting from the com- 
mon network into some prominent organ, and returning 
after forming one or more loops, as in the papillae of the 
tongue and skin. Whatever be the form of the capillary 
network in any tissue or organ, it is, as a rule, found to 
prevail in the corresponding parts of all animals. 

The number of the capillaries and the size of the meshes 
in different parts determine in general the degree of 
vascularity of those parts. The parts in which the net- 
work of capillaries is closest, that is, in which the meshes 
or interspaces are the smallest, are the lungs and the 
choroid membrane of the eye. In the iris and ciliary body 
the interspaces are somewhat wider, yet very small. In the 
human liver, the interspaces are of the same size, or even 
smaller than the capillary vessels themselves. In the human 
lung they are smaller than the vessels ; in the human 
kidney, and in the kidney of the dog, the diameter of the 
injected capillaries, compared with that of the interspaces^ 
is in the proportion of one to four, or of one to three. 
The brain receives a very large quantity of blood; but 
the capillaries in which the blood is distributed through 
its substance are very minute, and less numerous than in 
some other parts. Their diameter, according to E. H. 
Weber, compared with the long diameter of the meshes, 
being in the proportion of one to eight or ten ; compared 
with the transverse diameter, in the proportion of one to 
four or six. In the mucous membranes — for example, in 
the conjunctiva — and in the cutis vera, the capillary vessels 
are much larger than in the brain, and the interspaces 
narrower — namely, not more than three or four times 
wider than the vessels. In the periosteum the meshes are- 
much larger. In the cellular coat of arteries, the width 
of the meshes is ten times that of the vessels (Henle). 

It may be held as a general rule, that the more active 
the functions of an organ are, the more vascular it is ; that 
is, the closer is its capillary network and the larger its 



i6o 



THE CIRCULATIOX. 



supply of blood. Hence, the narrowness of the interspaces 
in all glandular organs, in mucous membranes, and in 
growing parts ; their much greater width in bones, liga- 
ments, and other very tough and comparatively inactive 
tissues ; and the complete absence of vessels in cartilage, 
the dense tendons of adults, and such' parts as those in 
which, probably, very little organic change occurs after 
they are once formed. But the general rule must be 
modified by the consideration, that some organs, such as 
the brain, though they have small and not very closely 
arranged capillaries, may receive large supplies of blood 
by reason of its more rapid movement. When an organ 
has large arterial trunks and a comparatively small supply 
of capillaries, the movement of the blood through it will 
be so quick, that it may, in a given time, receive as much 
fresh blood as a more vascular part with smaller trunks, 
though at any given instant the less vascular part will have 
in it a smaller quantity of blood. 

In the Circulation in the Capillaries, as seen in any trans- 
^'ig- 52-* parent part of a living adult 

animal by means of the mi- 
croscope (fig. 52), the blood 
flows with a constant equable 
motion. In very young ani- 
mals, the motion, though 
continuous, is accelerated at 
intervals corresponding to 
the pulse in the larger ar- 
teries, and a similar mo- 
tion of the blood is also 
seen in the capillaries of adtilt animals when they 
are feeble : if their exhaustion is so great that the 
power of the heart is still more diminished, the red cor- 
puscles are observed to have merely the periodic motion. 




Fig. 52. Capillaries in the web of the frog's foot magnified. 



THE CAPILLARIES. l6r 

and to remain stationary in the intervals; while, if the 
debility of the animal is extreme, they even recede some- 
what after each impulse, apparently because of the elasti- 
-city of the capillaries, and the tissues around them. These 
observations may be added to those already advanced 
(p. 132) to prove that, even in the state of great debility, 
the action of the heart is sufficient to impel the blood 
through the capillary vessels. Moreover, Dr. Marshall 
Hall having placed the pectoral fin of an eel in the field of 
the microscope and compressed it by the weight of a heavy 
probe, observed that the movement of the blood in the 
capillaries became obviously pulsatory, the pulsations being 
synchronous with the contractions of the ventricle. The 
pulsatory motion of the blood in the capillaries cannot be 
attributed to an action in these vessels; for, when the 
animal is tranquil, they present not the slightest change in. 
their diameter. 

It is in the capillaries, that the chief resistance is ofiered 
to the progress of the blood ; for in them the friction of 
the blood is greatly increased by the enormous multipli- 
cation of the surface with which it is brought in contact. 
The velocity of the blood is also in them reduced to its 
minimum, because of the widening of the stream. If, as 
Professor Miiller says, the sectional area of all the branches 
of a vessel imited were always the same as that of the 
vessel from which they arise, and if the aggregate sec- 
tional area of the capillary vessels were equal to that of 
the aorta, the mean rapidity of the blood's motion in the 
capillaries would be the same as in the aorta and largest 
^ arteries ; and if a similar correspondence of capacity existed 
^^'^ in the veins and arteries, there would be an equal cor- 
^ respondence in the rapidity of the circulation in them. It 

is quite true, that the force with which the blood is pro- 
pelled in the arteries, as shown by the quantity of blood 
which escapes from them in a certain space of time, is 
greater than that with which it moves in the veins ; 



1 62 THE CIRCULATION. 

"but tliis force has to overcome all the resistance offered ii* 
the arterial and capillary system — ^the heart itself, indeed, 
must overcome this resistance ; so that the excess of the 
force of the blood's motion in the arteries is expended in 
overcoming this resistance, and the rapidity of the circu- 
lation in the arteries, even from the commencement of the- 
aorta, would be the same as in the veins and capillaries, if 
the aggregate capacity of each of the three systems of 
Tessels were the same. 

But since the aggregate sectional area of the branches is 
greater than that of the trunk from which they arise, the 
rapidity of the blood's motion will necessarily be greater 
in the trunk, and will diminish in proportion as the 
aggregate capacity of the vessels increases during their 
ramification : in the same manner as, other things being 
equal, the velocity of a stream diminishes as it widens. 

The observations of Hales, E. H. Weber, and Valentin^ 
agree very closely as to the rate of the blood in the capil- 
laries of the frog : and the mean of their estimates gives 
the velocity of the systemic capillary circulation at about 
one inch per minute. Through the pulmonic capillaries, 
the rate of motion, according to Hales, is about five timea 
that through the systemic ones. The velocity in the 
capillaries of warm-blooded animals is greater, but has 
not y6t been accurately estimated. If it be assumed to be 
three times as great as in the frog, still the estimate may 
seem too low, and inconsistent with the facts, which show 
that the whole circulation is accomplished in about a 
minute. But the whole length of capillary vessels, through 
which any given portion of blood has to pass, probably 
does not exceed 3-Vth of an inch ; and therefore the time 
required for each quantity of blood to traverse its own 
appointed portion of the general capillary system will 
scarcely amount to a second : while in the pulmonic capil- 
lary system the length of time required will be much less- 
even than this. 



I 



THE CAPILLARIES. 1 63 

The estimates given above are drawn from observations 
of the movements of the red blood-corpuscles, which move 
in the centre of the stream. At the circumference of the 
stream, in contact with the walls of the vessel, and adhering 
to them, there is a layer of liquor sanguinis which appears 
to be motionless. The existence of this still layer, as it is 
termed, is inferred both from the general fact that such an 
one exists in all fine tubes traversed by fluid, and from 
what can be seen in watching the movements of the blood- 
corpuscles. The red corpuscles occupy the middle of the 
stream and move with comparative rapidity ; the colourless 
lymph- corpuscles run much more slowly by the walls of 
the vessel ; while next to the wall there is often a trans- 
parent space in which the fluid appears to be at rest ; for 
if any of the corpuscles happen to be forced within it, they 
move more slowly than before, rolling lazily along the side 
of the vessel, and often adhering to its wall. Part of this 
slow movement of the pale corpuscles and their occasional 
stoppage may be due, as E. H. Weber has suggested, to 
their having a natural tendency to adhere to the walls of 
the vessels. Sometimes, indeed, when the motion of the 
blood is not strong, many of the white corpuscles collect 
in a capillary vessel, and for a time entirely prevent the 
passage of the red corpuscles. But there is no doubt that 
such a still layer of liquor sanguinis exists next the walls 
of the vessels, and it is between this and the tissues around 
the vessels that those interchanges of particles take place 
which ensue in nutrition, secretion, and absorption by the 
blood-vessels ; interchanges which are probably facilitated 
by the tranquillity of the fluids between which they are 
effected. 

Until within the last few years it has been generally 
supposed that the occurrence of any transudation from the 
interior of the capillaries into the midst of the surrounding 
tissues was confined, in the absence of injury, strictly to the 
fluid part of the blood ; in other words, that the corpuscles 

M 2 



1 64 THE CIRCULATION. 

could not escape from the circulating stream, unless the 
waU of the containing blood-vessel were ruptured. It is 
true that an English physiologist, Dr. Augustus Waller, 
affirmed in 1846, that he had seen blood-corpuscles, both 
red and white, pass bodily through the wall of the capillary 
vessel in which they were contained; and that, as no opening 
could be seen before their escape, so none could be observed 
afterwards — so rapidly was the part healed. But these ob- 
servations did not attract much notice until the phenomena 
of escape of the blood-corpuscles from the capillaries and 
minute veins, apart from mechanical injury, was redis- 
covered by Professor Cohnheim in 1867. 

Professor Cohnheim' s experiment demonstrating the pass- 
age of the corpuscles through the wall of the blood-vessel, 
is performed in the following manner. A frog is curarized, 
that is to say, paralysis is produced by injecting under the 
skin a minute quantity of the poison called curare ; and 
the abdomen having been opened, a portion of small in- 
testine is drawn out, and its transparent mesentery spread 
out under a microscope. After a variable time, occupied 
by dilatation, following contraction, of the minute vessels, 
and accompanying quickening of the blood-stream, there 
ensues a retardation of the current ; and blood-corpuscles, 
both red and white, begin to make their way through the 
capillaries and small veins. The process of extrusion of 
the white corpuscles is thus described by Dr. Burden San- 
derson, and the passage of the red corpuscles occurs after 
much the same fashion. 

"Simultaneously with the retardation, the leucocjrtes, 
instead of loitering here and there at the edge of the axial 
current, begin to crowd in numbers against the vascular wall, 
as was long ago described by Dr. Williams. In this way 
the vein becomes lined with a continuous pavement of these 
bodies, which remain almost motionless, notwithstanding 
that the axial current sweeps by them as continuously as 
before, though with abated velocity. Now is the moment 



THE CAPILLAEIES. 165 

at which the eye must be fixed on the outer contour of the 
vessel, from which (to quote Professor Cohnheim's words) 
here and there minute, colourless, button-shaped elevations 
spring, just as if they w^ere produced by budding out of the 
wall of the vessel itself. The buds increase gradually and 
slowly in size, until each assumes the form of a hemispherical 
projection, of width corresponding to that of a leucocyte. 
Eventually the hemisphere is converted into a pear-shaped 
body, the small end of which is still attached to the surface 
of the vein, while the round part projects freely. Gradu- 
ally the little mass of protoplasm removes itself further and 
further away, and, as it does so, begins to shoot out delicate 
prongs of transparent protoplasm from its surface, in no- 
wise differing in their aspect from the slender thread by 
which it is still moored to the vessel. Finally the thread 
is severed, and the process is complete. The observer has 
before him an emigrant leucocyte, which in all appreciable 
respects resembles those which have been already described 
in the aqueous humour of the inflamed eye." 

Various explanations of these remarkable phenomena 
have been suggested. Probably the nearest to the truth 
are those which attribute the chief share in the process to 
the vital endowments with respect to mobility and contrac- 
tility of the parts concerned — both of the corpuscles 
(Bastian) and the capillary wall (Strieker). Dr. Sanderson 
remarks, *' the capillary is not a dead conduit, but a tube of 
living protoplasm. There is no difficulty in understanding 
how the membrane may open to allow the escape of leuco- 
cytes, and close again after they have passed out ; for it is 
one of the most striking peculiarities of contractile substance 
that when two parts of the same mass are separated, and 
again brought into contact, they melt together as if they 
had not been severed." 

Hitherto, the escape of the corpuscles from the interior 
of the blood-vessels into the surrounding tissues has been 
studied chiefly in connection with pathology. But it is im- 



1 66 THE CIRCULATION. 

possible to say, at present, to what degree the discovery 
may not influence all present notions regarding the nutri- 
tion of the tissues, even in health. 

The circulation through the capillaries must, of necessity, 
be largely influenced by that which occurs in the vessels on 
either side of them. — in the arteries or the veins ; their in- 
termediate position causing them to feel at once, so to speak, 
any alteration in the size or rate of the arterial or venous 
blood- stream. Thus, the apparent contraction of the 
capillaries, on the application of certain irritating sub- 
stances, and during fear, and their dilatation in blushing, 
may be referred to the action of the small arteries, rather 
than to that of the capillaries themselves. But largely as 
the capillaries are influenced by these, and by the con- 
ditions of the parts which surround and support them, 
their own endowments must not be disregarded. They 
must be looked upon, not as mere passive canals for 
the passage of blood, but as possessing endowments of 
their own, in relation to the circulation. The capillary 
wall is, according to Strieker, actively living and con- 
tractile ; and there is no reason to doubt that, as such, it 
must have an important influence in connection with that 
nutritive exchange which goes on without cessation be- 
tween the blood within and the tissues outside the capillary 
vessel ; a process which, under the name of vital capillary 
force, has long been recognised as one of the means con- 
cerned in the circulation of the blood. 

The results of morbid action, as well as the phenomena of 
health, strongly support the notion of the existence of 
this so-called vital capillary attraction between the 
blood and the tissues. For example, when the access 
of oxygen to the lungs is prevented, the circulation 
through the pulmonic capillaries is gradually retarded, the 
blood-corpuscles cluster together, and their movement is 
eventually almost arrested, even while the action of the 
heart continues. In inflammation, also, the capillaries of 



THE VEIXS. 167 

an inflamed part are enlarged and distended with blood, 
whicli either moves very slowly or is completely at rest. In 
both these cases the phenomena are local, and independent 
•of the action of the heart, and appear to result from some 
4ilteration in the blood, which increases the adhesion of its 
particles to one another, and to the walls of the capillaries, 
to an amount which the propelling action of the heart is 
not able to overcome. 

It may be concluded then, that the capillaries, which are 
formed of a simple cellular membrane, can of themselves 
exercise no such direct influence on the movement of their 
-contents as to be at all comparable in degree to that which 
■is exercised by the arteries or veins : yet that the constant 
interchange of relations between the blood within and the 
tissues outside these vessels does in some measure facilitate 
the movement of blood through the capillary system, and 
■constitute one of the assistant forces of the circulation. 

THE VEIXS. 

In structure the coats of veins bear a general resemblance 
to those of arteries. Thus, they possess an outer, middle, 
and internal coat. The outer coat is constructed of areolar 
-tissue like that of the arteries, but is thicker. In some 
Teins it contains muscular fibre-cells. 

The middle coat is considerably thinner than that of the 
•arteries ; and, although it contains circular unstriped mus- 
•cular fibres or fibre-cells, these are mingled with a larger 
proportion of yellow elastic and white fibrous tissue. In 
rthe large veins near the heart, namely, the vetKB cavce and 
pulmonary veins, the middle coat is replaced, for some 
^distance from the heart, by circularly arranged striped 
muscular fibres, continuous with those of the auricles. 

The internal coat of veins is less brittle than the corre- 
-.spending coat of an artery, but in other respects resembles 
it closely. 

The chief influence which the veins have in the circula- 



i68 



THE CIRCULATION. 



tion, is effected -with' the help'of the valves, which are placed 
in aU veins' subject to local pressure from the muscles- 
between or near which they run. The general construction 
of these valves is similar to that of the semilunar valves of 
the aorta and pulmonary artery, already described (p. 1 08) ;. 
but their free margins are turned in the opposite direction,. 
i.e. toivards the heart, so as to stop any movement of blood 
backward in the veins. They are commonly placed in pairs^ 
at various distances in different veins, but almost uniformly 
in each (fig. 5 3). In the smaller veins, single valves are- 
often met with ; and three or four are sometimes placed 
together, or near one another, in the largest veins, such as> 
the subclavian, and at their junction with the jugular veins. 
^^9- 53* '^^^ valves are semi- 

j\. B ^^ lunar; the unattached 

edge being in some^ 
examples concave, in 
others straight. They 
are composed of inex- 
tensile fibrous tissue, 
and are covered with 
epithelium like that 
lining the veins. 
During the 'period of 
their inaction, when 
the venous blood is flowing in its proper direction, they 
lie by the sides of the veins ; but when in action, they close- 
together Hke the valves of the arteries, and offer a com- 
plete barrier to any backward movement of the blood 
(figs. 54 and 55). 

Valves are not equally numerous in all veins, and ia 




* Fig- 53- Diagrams showing valves of veins. A. Part of a vein laid 
open and spread out, with two pairs of valves. B. Longitudinal sectioa 
of a vein, showing the apposition of the edges of the valves in their 
closed state. C. Portion of a distended vein, exhibiting a swelling in. 
the situation of a pair of valves. 



I 



VALVES OF VEINS. 1 69 

many they are absent altogether. They are most numerous 
in the veins of the extremities, and more so in those of the 
leg than the arm. They are commonly absent in veins of 
less than a line in diameter, and, as a general rule, there 
are few or none in those which are not subject to muscular 
pressure. Among those veins which have no valves may b& 
mentioned the superior and inferior vena cava, the trunk 
and branches of the portal vein, the hepatic and renal 
veins, and the pulmonary veins ; those in the interior 
of the cranium and vertebral column, those of the bones, 
and the trunk and branches of the umbilical vein are also 
destitute of valves. 

The principal obstacle to the circulation is already over- 
come when the blood has traversed the capillaries ; and the- 
force of the heart which is not yet consumed, is sufficient 
to complete its passage through the veins, in which tha 
obstructions to its movement are very slight. For the for- 
midable obstacle supposed to be presented by the gravita- 
tion of the blood, has no real existence, since the pressure 
exercised by the column of blood in the arteries, will be 
always sufficient to support a column of venous blood of the 
same height as itself : the two columns mutually balancing 
each other. Indeed, so long as both arteries and veins con- 
tain continuous columns of blood, the force of gravitation, 
whatever be the position of the body, can have no power ta 
move or resist the motion of any part of the blood in any 
direction. The lowest blood-vessels have, of course, to bear 
the greatest amount of pressure ; the pressure on each part 
being directly proportionate to the height of the column of 
blood above it : hence their liability to distension. But 
this pressure bears equally on both arteries and veins, and 
cannot either move, or resist the motion of, the fluid they 
contain, so long as- the columns of fluid are of equal height 
in both, and continuous. Their condition may, in this respect 
be compared with that of a double bent tube, full of fluid, 
held vertically ; whatever be the height and gravitation of 



a 70 THE CIRCULATION. 

the columns of fluid, neitlier of tliem can move of its own 
weight, each being supported by the other ; yet the least 
pressure on the top of either column will lift up the other : 
«o, when the body is erect, the least pressure on the column 
of arterial blood may lift up the venous blood, and, were 
it not for the valves, the least pressure on the venous might 
lift up the arterial column. 

In experiments to determine what proportion of the force 
of the left ventricle remains to propel the blood in the veins, 
Valentin found that the pressure of the blood in the jugular 
vein of a dog, as estimated by the hsemadynamometer, did 
not amount to more than Jy or -Jj of that in the carotid 
artery of the same animal ; and this estimate is confirmed, 
in the instances of several other arteries and their corre- 
sponding veins, by ^Mogk. In the upper part of the inferior 
vena cava, Valentin could scarcely detect the existence of 
any pressure, nearly the whole force received from the heart 
having been, apparently, consumed during the passage of 
the blood through the capillaries. But slight as this re- 
maining force might be (and the experiment in which it 
was estimated would reduce the force of the heart below 
its natural standard), it would be enough to complete 
the circulation of the blood; for, as already stated, the 
spontaneous dilatation of the auricles and ventricles, though 
it may not be forcible enough to assist the movement of 
blood into them, is adapted to ofier to that movement no 
obstacle. 

Very effectual assistance to the flow of blood in the veins 
is afibrded by the action of the muscles capable of pressing 
on such veins as have valves. 

The effect of muscular pressure on such veins may be thus 
•explained. When pressure is applied to any part of a vein, 
^nd the current of blood in it is obstructed, the portion 
behind the seat of pressure becomes swollen and distended 
as far back as to the next pair of valves. These, acting like 
•the arterial valves, and being, like them, inextensile both in 



PRESSURE IX VEINS. 



171 



I 



themselves and at their margins of attachment, do not 
follow the vein in its distension, but are drawn out towards 
the axis of the canal. Then, if the pressure continues on 
the vein, the compressed blood, tending to move equally in 
all directions, presses the valves down into contact at their 
free edges, and they close the vein and prevent regurgita- 
tion of the blood. Thus, whatever force is exercised by 
the pressure of the muscles on the veins, is distributed partly 
in pressing the blood onwards in the proper course of the 
circulation, and partly in pressing it backwards and closing 
the valves behind. 

The circulation might lose as much as it gains by such 
compression of the veins, if it were not for the numerous 
anastomoses by which they communicate, one with another ; 



Fig. 54* 



Fig. 55.t 




for through these, the closing up of the venous channel by 
the backward pressure is prevented from being any serious 



* Fig. 54. Vein with valves open (Dalton). 

t Fig. 55. Vein with valves closed ; stream of blood passing off by 
lateral channel (Dalton). 



172 THE CIECULATIOX. 

hindrance to the circulation, since the blood, of which the 
onward course is arrested by the closed valves, can at once 
pass through some anastomosing channel, and proceed on its 
way by another vein (figs. 54 and 55). Thus, therefore, the 
effect of muscular pressure upon veins which have valves, is 
turned almost entirely to the advantage of the circulation; 
the pressure of the blood onwards is all advantageous, and 
the pressure of the blood backwards is prevented from being 
a' hindrance by the closure of the valves and the anastomoses 
of the veins. 

The effects of such muscular pressure are well shown by 
the acceleration of the stream of blood when, in venesec- 
tion, the muscles of the fore-arm are put in action, and by 
the general acceleration of the circulation during active 
exercise; and the numerous movements which are con- 
tinually taking place in the body while awake, though 
their single effects may be less striking, must be an im- 
portant auxiliary to the venous circulation. Yet they 
are not essential ; for the venous circulation continues 
unimpaired in parts at rest, in paralysed limbs, and in 
parts in which the veins are not subject to any muscular 
pressure. 

Besides the assistance thus afforded by muscular pressure 
to the movement of blood along veins possessed of valves, 
it has been discovered by Mr. Wharton Jones that, in the 
web of the bat's wing, the veins are furnished with valves, 
and possess the remarkable property of rhythmical contrac- 
tion and a dilatation, whereby the current of blood within 
them is distinctly accelerated. The contraction occurred, 
on an average, about ten times in a minute ; the existence 
of valves preventing regurgitation, the entire effect of the 
contractions was auxiliary to the onward current of blood. 
Analogous phenomena have been now frequently observed 
in other animals. 



EFFECTS OF EESPIRATIOX. 173 



Agents Concerned in the Circulation of the Blood. 

The agents concerned in the circulation of the blood 
which have been now described, may be thus enume- 
rated : — 

1 . The action of the heart and of the arteries. 

2. The vital capillary force exercised in the capil- 
laries. 

3. The possible slight action of the muscular coat of 
veins ; and, much more, the contraction of muscles capable 
of acting on veins provided with valves. 

It remains only to consider (4) the influence of the 
respiratory movements on the circulation. 

Although the continuance of the respiratory movements 
is essential to the circulation of the blood, and although 
their cessation is followed, within a very few minutes, by 
that of the heart's action also, yet their direct mechanical 
influence on the movement of the current of blood is pro- 
bably, under ordinary circumstances, but slight. The effect 
of expiration in increasing the pressure of the blood in the 
arteries is minutely illustrated by the experiments of Lud- 
wig. It acts as the pressure of contracting muscles does 
upon the veins, and is advantageous to the onward move- 
ment of arterial blood, inasmuch as all movement backwards 
into the heart, which would otherwise occur at the same 
moment and from the same cause, is prevented by the force 
of the onward stream of blood from the contracting ven- 
tricle, and in the intervals of this contraction by the closure 
of the semilunar valves. Under ordinary circumstances, 
and with a free passage through the capillaries of the lungs, 
the effect of expiration on the stream of blood in the veins 
is also probably to assist, rather than retard its movement 
in the proper direction. For, with no obstruction in front, 
there is the force of the blood streaming into the heart from 
behind, to prevent any tendency to a backward flow, even 



174 



THE CIRCULATIOX. 



apart from what may be effected by tlie presence of the 
valves of the venous system. 

It is true that in violent expiratorj^ efforts there is a 
certain retardation of the circulation in the veins. The 
effect of such retardation is shown in the swelling-up of 
the veins of the head and neck, and the lividity of the face, 
during coughing, straining, and similar violent expiratory 
efforts ; the effects shown in these instances being due both 
to some actual regurgitation of the blood in the great 
veins, and to the accumulation of blood in all the veins, from 
their being constantly more and more filled by the influx 
from the arteries. 

But strong expiratory efforts, as in straining and the 
like, are not fairly comparable to ordinary expiration, inas- 
much as they are instances of more or less interference 
with expiration, and involve probably circumstances lead- 
ing to obstruction of the circulation in the pulmonary 
capillaries, such as are not present in the ordinary rhyth- 
mical exit of air from the lungs. 

The act of inspiration is favourable to the venous circu- 
lation, and its effect is not counterbalanced by its tendency 
to draw the arterial, as well as the venous, blood towards 
the cavity of the chest. When the chest is enlarged in 
inspiration, the additional space within it is filled chiefly 
by the fresh quantity of air which passes through the 
trachea and bronchial passages to the vesicular structure 
of the lungs. But the blood being, like the air, subject to 
the atmospheric pressure, some of it also is at the same time 
pressed towards the expanding cavity of the chest, and 
therein towards the heart. The effect of this on the arterial 
current is hindered by the aortic valves, while they are 
closed, and by the forcible outward stream of blood from* 
the ventricles when they are open; while, on the other 
hand, there is nothing to prevent an increased afilux of 
blood to the auricles through the large veins. 

Sir David Barry was the first who showed plainly this- 



VELOCITY OF THE CIRCULATION. 175 

effect of inspiration on the venous circulation; and he- 
mentions the following experiment in proof of it. He 
introduced one end of a bent glass tube into the jugular- 
vein of an animal, the vein being tied above the point 
where the tube was inserted ; the inferior end of the tube- 
was immersed in some coloured fluid. He then observed 
that at the time of each inspiration the fluid ascended iii 
the tube, while during expiration it either remained 
stationary, or even sank. Poiseuille confirmed the truth 
of this observation, in a more accurate manner, by means of 
his heemadynamometer. And a like confirmation has been? 
since furnished by Valentin, and in minute details by Ludwig.. 
The effect of inspiration on the veins is observable only 
in the large ones near the thorax. Poiseuille could not 
detect it by means of his instrument in veins more distant 
from the heart, — for example, in the veins of the extremi- 
ties. And its beneficial effect would be neutralized were- 
it not for the valves ; for he found that, when he repeated 
Sir D. Barry's experiments, and passed the tube so far 
along the veins that it went beyond the valves nearest to* 
the heart, as much fluid was forced back into the tube in- 
every expiration as was drawn in through it in every 
inspiration. 

Dr. Burden Sanderson's experiments have proved more 
directly that inspiration is favourable to the circulation^ 
inasmuch as, during it, the tension of the arterial system 
is increased. And it is only when the respiratory orifice 
is closed, as by plugging the trachea, that inspiratory 
efforts are sufficient to produce an opposite effect — to 
diminish the tension in the arteries. 

On the whole, therefore, the respiratory movements of 
the chest are advantageous to the circulation. 

Velocity of Blood in the Veins. 

The velocity of the blood is greater in the veins than in 
the capillaries, but less than in the arteries ; and with this 



176 THE CIECULATIOX. 

fact may be remembered tlie relative capacities of the 
arterial and venous systems ; for since the veins return to 
the heart all the blood that they receive from it in a given 
time through the arteries, their larger size and propor- 
tionally greater number must compensate for the slower 
movement of the blood through them. If an accurate 
estimate of the proportionate areas of arteries and the veins 
corresponding to them could be made, we might, from the 
velocity of the arterial current, calculate that of the venous. 
An usual estimate is, that the capacity of the veins is about 
twice or three times as great as that of the arteries, and 
that the velocity of the blood's motion is, therefore, about 
twice or three times as great in the arteries as in the veins. 
Some doubt has, however, been lately expressed regarding 
the accuracy of this calculation, and the matter, therefore, 
must be considered not yet settled. The rate at which the 
blood moves in the veins gradually increases the nearer it 
approaches the heart, for the sectional area of the venous 
trunks, compared with that of the branches opening into 
them, becomes gradually less as the trunks advance towards 
the heart. 

Velocity of the Circulation. 

Having now considered the share which each of the cir- 
culatory organs has in the propulsion and direction of the 
blood, we may speak of their combined effects, especially 
in regard to the velocity with which the movement of the 
blood through the whole round of the circulation is accom- 
plished. As Miiller says, the rate of the blood's motion in 
the vessels must not be judged of by the rapidity with 
which it flows from a vessel when divided. In the latter 
case, the rate of motion is the result of the entire pressure 
to which the whole mass of blood is subjected in the vas- 
cular system, and which at the point of the incision in the 
vessel meets with no resistance. In the closed vessels, on 
the contrary, no portion of blood can be moved forwards 



TELOCITY OF THE CIRCULATION. 177 

except by impelling on the whole mass, and by overcoming 
the resistance arising from friction in the smaller vessels. 

From the rate at which the blood escapes from opened 
vessels we can only judge, in general, that its velocity is, as 
already said, greater in arteries than in veins, and in both 
these greater than in the capillaries. More satisfactory data 
for the estimates are afforded by the results of experiments 
to ascertain the rapidity with which poisons introduced 
into the blood are transmitted from one part of the vascular 
system to another. From eighteen such experiments on 
horses, Hering deduced that the time required for the 
passage of a solution of ferrocyanide of potassium, mixed 
with the blood, from one jugular vein (through the right 
side of the heart, the pulmonary circulation, the left cavities 
of the heart, and the general circulation) to the jugular 
vein of the opposite side, varies from twenty to thirty 
seconds. The same substance was transmitted from the 
jugular vein to the great saphena in twenty seconds; from 
the jugular vein to the masseteric artery, in between fifteen 
and thirty seconds ; to the facial artery, in one experiment, 
in between ten and fifteen seconds ; in another experiment 
in between twenty and twenty-five seconds ; in its transit 
from the jugular vein to the metatarsal artery, it occupied 
between twenty and thirty seconds, and in one instance 
more than forty seconds. The result was nearly the same 
whatever was the rate of the heart's action. 

Poiseuille's observations accord completely with the 
above, and show, moreover, that when the ferrocyanide 
is injected into the blood with other substances, such as 
acetate of ammonia, or nitrate of potash (solutions of 
which, as other experiments have shown, pass quickly 
through capillary tubes), the passage from one jugular 
vein to the other is effected in from eighteen to twenty- 
four seconds ; while, if instead of these, alcohol is added, 
the passage is not completed until from forty to forty-five 
seconds after injection. Still greater rapidity of transit 



178. THE CIRCULATIOX. 

lias been observed by Mr. J. Blake, wbo found that 
nitrate of baryta injected into the jugular vein of a horse 
could be detected in blood drawn from the carotid artery 
of the opposite side in from fifteen to twenty seconds after 
the injection. In sixteen seconds a solution of nitrate of 
potash, injected into the jugular vein of a horse, caused 
complete arrest of the heart's action, by entering and 
diffusing itself through the coronary arteries. In a dog, 
the poisonous effects of strychnia on the nervous system 
were manifested in twelve seconds after injection into the 
jugular vein ; in a fowl, in six and a half seconds, and in 
a rabbit in four and a half seconds. 

In all these experiments, it is assumed that the sub- 
stance injected moves with the blood, and at the same rate 
as it, and does not move from one part of the organs of 
circulation to another by diffusing itself through the blood 
or tissues more quickly than the blood moves. The 
assumption is sufficiently probable, to be considered nearly 
certain, that the times above mentioned, as occupied in 
the passage of the injected substances, are those in which 
the portion of blood, into which each was injected, was 
carried from one part to another of the vascular system. 
It would, therefore, appear that a portion of blood can 
traverse the entire course of the circulation, in the horse, 
in half a minute ; of course it would require longer to 
traverse the vessels of the most distant part of the ex- 
tremities than to go through those of the neck; but taking 
an average length of vessels to be traversed, and assuming, 
as we may, that the ^movement of blood in the human 
subject is not slower than in the horse, it may be concluded 
that one minute, which is the estimate usually adopted 
of the average time in which the blood completes its entire 
circuit in man, is rather above than below the actual rate. 

Another mode of estimating the general velocity of the 
circulating blood, is by calculating it from the quantity of 
blood supposed to be contained in the body, and from the 



VELOCITY OF THE CIRCULATIOX. 



179 



•quantity wliicli can pass through, the heart in each of its 
actions. But the conchisions arrived at by this method 
are less satisfactory. For the estimates both of the total 
quantity of blood, and of the capacity of the cavities of 
the heart, have as yet only approximated to the truth. 
StiU, the most careful of the estimates thus made accord 
with those already mentioned ; for Valentin has, from 
these data, calculated that the blood may all pass through 
the heart in from 43 J to 62 § seconds. 

The estimate for the speed at which the blood may be 
seen moving in transparent parts, is not opposed to this. 
For, as already stated (p. 162), though the movement 
through the capillaries may be very slow, yet the length 
^f capillary vessel through which any portion of blood has 
to pass is very small. Even if we estimate that length at 
the tenth of an inch, and suppose the velocity of the blood 
therein to be only one inch per minute, then each portion 
of blood may traverse its own distance of the capillary 
system in about six seconds. There would thus be plenty 
of time left for the blood to travel through its circuit in 
the larger vessels, in which the greatest length of tube 
that it can have to traverse in the human subject does not 
exceed ten feet. 

All the estimates here given are averages ; but of course 
the time in which a given portion of blood passes from 
one side of the heart to the other, varies much according 
to the organ it has to traverse. The blood which circulates 
from the left ventricle, through the coronary vessels, to the 
right side of the heart, requires a far shorter time for the 
completion of its course than the blood which flows from 
the left side of the heart to the feet, and back again to the 
right side of the heart ; for the circulation from the left to 
the right cavities of the heart may be represented as form- 
ing a number of arches, varying in size, and requiring 
proportionately various times for the blood to traverse 
them ; the smallest of these arches being formed by the 

N 2 



l8o THE CIRCULATION. 

circulation through the coronary vessels of the heart itself- 
The course of the blood from the right side of the heart, 
through the lungs to the left, is shorter than most of the 
arches described by the systemic circulation, and in it the 
blood flows, ccBteris paribus, much quicker than in most of 
the vessels which belong to the aortic circulation. For 
although the quantity of blood contained, at any instant, 
in the greater circulation of the body, is far greater than 
the quantity within the lesser circulation; yet, in any given 
space of time, as much blood must pass through the lungs 
as passes in the same time through the systemic circulation. 
If the systemic vessels contain five times as much blood as^ 
the pulmonary, the blood in them must move five times as^ 
slow as in these ; else, the right side of the heart would, 
be either overfilled or not filled enough. 

Peculiarities of the Circulation in different Parts. 

The most remarkable peculiarities attending the circula- 
tion of blood through different organs are observed in the 
cases of the lungs, the liver, the brain, and the erectile organs. 
The pulmonary and portal circulations have been already 
alluded to (pp. lOl, I02), and will be again noticed w^hen 
considering the functions of the lungs and liver. 

The chief circumstances requiring notice, in relation to 
the cerebral circulation, are observed in the arrangement and 
distribution of the vessels of the brain, and in the con- 
ditions attending the amount of blood usually contained 
within the cranium. 

The functions of the brain seem to require that it should 
receive a large supply of blood. This is accomplished 
through the number and size of its arteries, the two internal 
carotids, and the two vertebrals. But it appears to be 
further necessary that the force with which this blood is 
sent to the brain should be less, or at least, subject to less 
variation from external circumstances, than it is in other 
parts. This object is effected by several provisions ; such 



CEREBRAL CIRCULATION. i8l 

as the tortuosity of the large arteries, and their wide anas- 
tomoses in the formation of the circle of Willis, which will 
insure that the supply of blood to the brain may be uni- 
form, though it may by an accident be diminished, or 
in some way changed, through one or more of the principal 
arteries. The transit of the large arteries through bone, 
-especially the carotid canal of the temporal bone, may 
prevent any undue distension; and uniformity of supply 
is further insured by the arrangement of the vessels in 
the pia mater, in which, previous to their distribution to 
the substance of the brain, the large arteries break up and 
■divide into innumerable minute branches ending in capil- 
laries, which, after frequent communications with one 
another, enter the brain, and carry into nearly every part 
>9f it uniform and equable streams of blood. 

The arrangement of the veins within the cranium is also 
peculiar. The large venous trunks or sinuses are formed 
so as to be scarcely capable of change of size ; and com- 
posed, as they are, of the tough tissue of the dura mater, 
and, in some instances, bounded on one side by the bony 
cranium, they are not compressible by any force which the 
fulness of the arteries might exercise through the substance 
of the brain ; nor do they admit of distension when the 
flow of venous blood from the brain is obstructed. 

The general uniformity in the supply of blood to the 
brain, which is thus secured, is well adapted, not only to 
its functions, but also to its condition as a mass of nearly 
incompressible substance placed in a cavity with unyielding 
walls. These conditions of the brain and skull have ap- 
peared, indeed, to some, enough to justify the opinion 
•that the quantity of blood in the brain must be at all times 
the same ; and that the quantity of blood received within 
^ny given time through the arteries must be always, and 
at the same time, exactly equal to that removed by the 
veins. In accordance with this supposition, the symptoms 
commonly referred to either excess or deficiency of blood 



1 82 THE CIRCULATIOX. 

in the "brain, were ascribed to a disturbance in the balance- 
between the quantity of arterial and that of venous blood. 
Some experiments performed by Dr. Kellie appeared ta 
establish the correctness of this view. But Dr. Burrows 
having repeated these experiments, and performed addi- 
tional ones, obtained different results. He found that in 
animals bled to death, without any aperture being made 
in the cranium, the brain became pale and anaemic like 
other parts. And in proof that, during life, the cerebral 
circulation is influenced by the same general circumstances- 
that influence the circulation elsewhere, he found conges- 
tion of the cerebral vessels in rabbits killed by strangling 
or drowning ; while in others, killed by prussic acid, h& 
observed that the quantity of blood in the cavity of the 
cranium was determined by the position in which the 
animal was placed after death, the cerebral vessels being 
congested when the animal was suspended with its head 
downwards, and comparatively empty when the animal 
was kept suspended by the ears. He concluded, therefore,, 
that although the total volume of the contents of the 
cranium is probably nearly always the same, yet the 
quantity of blood in it is liable to variation, its increase or 
diminution being accompanied by a simultaneous diminu- 
tion or increase in the quantity of the cerebro- spinal fluid, 
which, by readily admitting of being removed from one 
part of the brain and spinal cord to another, and of being 
rapidly absorbed, and as readily efiused, would serve as a 
kind of supplemental fluid to the other contents of the 
cranium, to keep it uniformly filled in case of variations in 
their quantity. And there can be no doubt that, although 
the arrangements of the blood-vessels, to which reference 
has been made, ensure to the brain an amount of blood 
which is tolerably uniform, yet, inasmuch as with every 
beat of the heart and every act of respiration, and under 
many other circumstances, the quantity of blood in the 
cavity of the cranium is constantly varying, it is plain that,, 



CIRCULATION IX ERECTILE STRUCTUKES. 183 

were there not provision made for the possible displace- 
ment of some of the contents of the unyielding bony 
case in which the brain is contained, there would be often 
alternations of excessive pressure with insufficient supply 
of blood. Hence we may consider that the cerebro-spinal 
fluid in the interior of the skull not only subserves the 
mechanical functions of fat in other parts as a packing 
material, but by the readiness with which it can be dis- 
placed into the spinal canal, provides the means whereby 
undue pressure and insufficient supply of blood are equally 
prevented. 

Circulation in erectile structures. — The instances of greatest 
variation in the quantity of blood contained, at different 
times, in the same organs, are found in certain structures 
which, under ordinary circumstances, are soft and flaccid, 
but, at certain times, receive an unusually large quantity 
of blood, become distended and swollen by it, and pass into 
the state which has been termed erection. Such structures 
are the corpora cavernosa and corpus spongiosum of the 
penis in the male, and the clitoris in the female ; and, to 
a less degree, the nipple of the mammary gland in both 
sexes. The corpus cavernosum penis, which is the best 
example of an erectile structure, has an external fibrous 
membrane or sheath ; and from the inner surface of the 
latter are prolonged numerous fine lamellae which divide 
its cavity into small compartments looking like cells when 
they are inflated. Within these is situated the plexus of 
veins upon which the peculiar erectile property of the 
organ mainly depends. It consists of short veins which 
very closely interlace and anastomose with each other in 
all directions, and admit of great variation of size, col- 
lapsing in the passive state of the organ, but, for erection, 
capable of an amount of dilatation which exceeds beyond 
comparison that of the arteries and veins which convey the 
blood to and from them. The strong fibrous tissue lying 
in the intervals of the venous plexuses, and the external 



I 84 THE CIRCULATION. 

fibrous membrane or sheath with which it is connected, 
limit the distension of the vessels, and, during the state of 
erection, give to the penis its condition of tension and 
firmness. The same general condition of vessels exists in 
the corpus spongiosum urethrse, but around the urethra 
the fibrous tissue is much weaker than around the body of 
the penis, and around the glands there is none. The 
venous blood is returned from the plexuses by compara- 
tively small veins ; those from the glans and the fore part 
of the urethra empty themselves into the dorsal vein of the 
penis ; those from the corpus cavernosum pass into deeper 
veins which issue from the corpora cavernosa at the crura 
penis ; and those from the rest of the urethra and bulb 
pass more directly into the plexus of the veins about the 
prostate. For aU these veins one condition is the same ; 
namely, that they are liable to the pressure of muscles 
when they leave the penis. The muscles chiefly con- 
cerned in this action are the erector penis and accelerator 
urina). 

Erection results from the distension of the venous plex- 
uses with blood. The principal exciting cause in the erec- 
tion of the penis is nervous irritation, originating in the 
part itself, or derived from the brain and spinal cord. The 
nervous influence is communicated to the penis by the pudic 
nerves, which ramify in its vascular tissue : and Guenther 
has observed, that, after their division in the horse, the 
penis is no longer capable of erection. It affords a good 
example of the subjection of the circulation in an indivi- 
dual organ to the influence of the nerves ; but the mode 
in which they excite a greater influx of blood is not with 
certainty known. 

The most probable explanation is that offered by Pro- 
fessor Kolliker, who ascribes the distension of the venous 
plexuses to the influence of organic muscular fibres, which 
are found in abundance in the corpora cavernosa of the 
penis, from the bulb to the glans, also in the clitoris and 




\ 



CIRCULATION IX ERECTILE STRUCTURES. 185 

other parts capable of erection. While erectile organs 
are flaccid and at rest, these contractile fibres exercise an 
amount of pressure on the plexuses of vessels distributed 
amongst them, sufficient to prevent their distension with 
blood. But when through the influence of their nerves, 
these parts are stimulated to erection, the action of these 
fibres is suspended, and the plexuses thus liberated from 
pressure, yield to the distending force of the blood, which, 
probably, at the same time arrives in greater quantity, 
owing to a simultaneous dilatation of the arteries of the 
parts, and thus the plexuses become filled, and remain so 
until the stimulus to erection subsides, when the organic 
muscular fibres again contract, and so gradually expel the 
excess of blood from the previously distended vessels. 
The influence of cold in producing extreme contraction and 
shrinking of erectile organs, and the opposite effect of 
warmth in inducing fulness and distension of these parts, 
are among the arguments used by Kolliker in support of 
this opinion. 

The accurate dissections and experiments of Kobelt, 
extending and confirming those of Le Gros Clark and 
Krause, have shown, that this influx of the blood, however 
explained, is the first condition necessary for erection, and 
that through it alone much enlargement and turgescence 
of the penis may ensue. But the erection is probably 
not complete, nor maintained for any time except when, 
together with this influx, the muscles already mentioned 
contract, and by compressing the veins, stop the efflux of 
blood, or prevent it from being as great as the influx. 

It appears to be only the most perfect kind of erection 
that needs the help of muscles to compress the veins ; and 
none such can materially assist the erection of the nipples, 
or that amount of turgescence, just falling short of erec- 
tion, of which the spleen and many other parts are capable. 
For such turgescence nothing more seems necessary than 
a large plexiform arrangement of the veins, and such 



1 86 EESPIRATION. 

arteries as may admit, upon local occasions, augmented 
quantities of blood. 

The Influence of the Nervous System on the circulation 
in the blood-vessels will be considered in Chap. XVII. 



CHAPTEil VII. 



KESPIKATION. 



As the blood circulates through the various parts of the 
body, and fulfils its office by nourishing the several 
tissues, by supplying to secreting organs the materials 
necessary for their secretions, and by the performance of 
other duties with which it is charged, it is deprived of 
part of its nutritive constituents, and receives impurities 
which need removal from the body. It is, therefore, 
necessary that fresh supplies of nutriment should be con- 
tinually added to the blood, and that provision should 
be made for the removal of the impurities. The first of 
these objects is accomplished by the processes of digestion 
and absorption. The second is principally effected by the 
agency of the various excretory organs, through which are 
removed the several impurities with which the blood is 
charged, whether these impurities are derived altogether 
from the degenerations of tissue, or in part also from the 
elements of unassimilated food. One of the most important 
and abundant of the impurities is carbonic acid, the re- 
moval of which and the introduction of fresh quantities of 
oxygen, constitute the chief purpose of respiration — a 



STRUCTURE OF THE LUNGS. 



187 



process which, because of its intimate relation to the cir- 
culation, may be considered here, rather than with the 
other excretory functions. 



Position and Structure of the Lungs. 

The lungs occupy the greater portion of the chest, or 
uppermost of the two cavities into which the body is 
divided by the diaphragm (fig. 3 1 ). They are of a spongj' 
elastic texture, and on section appear to the naked eye as 
if they were in great part solid organs, except here and 
there, at certain points, where branches of the bronchi or 
air- tubes may have been cut across, and show, on their 
surface of the section, their tubular structure. 

In fact, however, the lungs are hollow organs, and we 
may consider them as really two bags containing air, each 
of which communicates by a separate orifice with a common 
air-tube (fig. 31), through the upper portion of which^ 
the larynx, they freely communicate with the external 

Fig. 56*. 




atmosphere. The orifice of the larynx is guarded by 
muscles, and can be opened or closed at will. 



* Fig. 56. Transverse section of the chest (after Gray). 



J 88 IlESPIRATION. 

It lias been said, in the preceding chapter that each 
lung is enveloped in a distinct fibrous bag, with a smooth, 
slippery lining, and that the outer smooth surface of the 
lung glides easily on the inner smooth surface of the 
bag which envelops it. This enveloping bag, which is 
•called the pleura, is easily seen in the dead subject ; and 
■when it is opened, as in an ordinary post-mortem examina- 
tion, there is a considerable space left, by the elastic recoil 
of the lung, between the outer surface of the lung and the 
inner surface of the pleura, which is left sticking, so to 
■speak, to the inner surface of the walls and floor of the 
<3hest. 

This space, however, between the lung and the pleura 
■does not exist (except in some cases of disease) so long as 
the chest is not opened ; and, while considering the subject 
of normal healthy respiration, we may discard altogether 
the notion of any space or cavity between the lung and 
the wall of the chest. So far as the movement of the lung 
is concerned it might be adherent completely to the chest- 
wall, inasmuch as they accompany each other in all their 
movements ; only there is a slight gliding of the smooth 
surface of the lung on the smooth inner surface of the 
pleura, but no separation, in the slightest degree, of one 
from the other.* 

The trachea, or tube through which air passes to the 
lungs, divides into two branches — one for each lung ; 
-and these primary branches, or bronchi, after entering the 



* It may be mentioned, that the smooth covering of the lung is 
o-eally continuous with tlie inner smooth lining of the walls and floor of 
the chest, as will be readily seen in fig. 56. Hence the membrane 
Avhich covers the lung is called the visceral layer of the pleum, and that 
which lines the walls and floor of the chest the xx^rietal layer. The 
Jippearance of a C4ivity or space (fig. 56) between the visceral layer of 
l)leura (covering the lungs) and the parietal layer (covering the inner 
surface of the wall of the chest and upper part of the diaphragm) is 
only inserted for the sake of distinctness. 



STllUCTUEE OF THE LUNGS. 189 

substance of the organ, divide and subdivide into a number 
of smaller and smaller branches, which penetrate to every 
part of the organ, until at length they end in the smaller 
subdivisions of the lung called lobules. All the larger 
branches have walls formed of tough membrane, contain- 
ing portions of cartilaginous rings, by which they are held 
open, and unstriped muscular fibres, as well as longi- 
tudinal bundles of elastic tissue. They are lined by 
mucous membrane, the surface of which, like that of the 

J'lrj. 57.* 




larynx and trachea, is covered with vibratile ciliary epi- 
thelium (fig. 58). 

As the bronchi divide they become smaller and smaller, 



* Fig. 57. A diagraniiiiatic representation of the heart and great 
vessels in connection with the lungs — ^. The pericardium has been 
removed, and the lungs are turned aside, i, right auricle ; 2, vena cava 
superior ; 3, vena cava inferior ; 4, right ventricle ; 5, stem of the pul- 
monary artery ; a a, its right and left branches ; 6, left auricular 
appendage ; 7, left ventricle ; 8, aorta ; 9, 10, the two lobes of the left 
lung ; II, 12, 13, the three lobes of the right lung ; b b, right and left 
bronchi ; v v, right and left upper pulmonary veins. 



I90 RESPIRATION. 

and their walls thinner; the cartilaginous rings, especially 
becoming scarcer and more irregular, until, in the smaller 
bronchial tubes, they are represented only by minute and 
scattered cartilaginous flakes. And when the bronchi, by 
successive branches, are reduced to about -^L of an inch 
in diameter, they lose their cartilaginous element alto- 
gether, and their waUs are formed only of a tough, fibrous, 
elastic membrane, with traces of circular muscular fibres; 
they are still lined, however, by a thin mucous membrane, 
with ciliated epithelium. 

Each lung is partially subdivided into separate portions, 
called lobes ; the ri ght lung, into three lobes, and the left 
lung into two (fig. 57). Each of these lobes, again, is 

Fui. 58.* 




-composed of a large number of minute parts, called lobules. 
Each pulmonary lobule may be considered a lung in 
miniature, consisting, as it does, of a branch of the bron- 
chial tube, of air-cells, blood-vessels, nerves, and lymphatics, 
with a sparing amount of areolar tissue. 

On entering a lobule, the small bronchial tube divides 



* Fig. 58. Ciliary epithelium of the human trachea magnified 350 
diameters, a, Layer of longitudinally arranged elastic fibres ; h, Base- 
ment membrane ; c, Deepest cells, circular in fomi ; d, Intermediate 
elongated cells ; e. Outermost layer of cells fully developed and bearing 
<;ilia (from Kolliker). 



STRIJCTURE OF THE LIIXGS. 



191 



Fig. 59.* 



and subdivides ; its walls, at the same time, becoming 
thinner and thinner, until at length they are formed only 
of a thin membrane of areolar and elastic tissue, lined by 
a layer of squamous epithelium, not provided with cilia. At 
the same tmie, they are altered in shape; each of the 
minute terminal branches widening out funnel- wise, and 
its walls being pouched out irregularly into small saccular 
dilatations, called air-cells (fig. 59)^ Such a funnel-shaped 
terminal branch of the bronchial tube, with its group of 
pouches or air-cells, has been called an bifundihulum 
(fig. 59), and the irregular oblong space in its centre, 
with which the air-cells communicate, an intercellular 
passage. 

The air-cells may be 
placed singly, like recesses 
from the intercellular pas- 
sage, but more often they 
are arranged in groups or 
even in rows, like minute 
sacculated tubes; so that 
a short series of cells, 
all communicating with 
one another, open by a 
common orifice into the 
tube. The cells are of 
various forms, according 
to the mutual pressure to 
which they are subject ; 
their walls are nearly in contact, and they vary from 
^Q to y\^ of an inch in diameter. Their walls are formed 
of fine membrane, similar to that of the intercellular 
passages, and continuous with it, which membrane is 




* Fig- 59- Two small groups of air-cells, or infundibula, a a, with 
air-cells, b b, and the ultimate bronchial tubes, c c, with which the air- 
cells communicate. From a new-born child (after Kolliker). 



1^2 EESPIRATIOX. 

folded on itself so as to form a sharp-edged border at 
each circular orifice of communication between contiguous 
air-cells, or between the cells and the ^bronchial passages. 
Numerous fibres of elastic tissue are spread out between 
contiguous air-cells, and many of these are attached to tlie 
outer surface of the fine membrane of which each cell is 
composed, imparting to it additional strength, and the 
power of recoil after distension (fig. 6o, b and c). The 

Fig. 60.* 




cells are lined by a layer of squamous or tessellated epithe- 
lium, not provided with cilia. Outside the cells, a net- 
work of pulmonary capillaries is spread out so densely 
(fig. 61), that the interspaces or meshes are even narrower 

* Fig. 60. Air-cells of lung, magnified 350 diameters, a, Epithelial 
lining of the cells ; b, Fibres of elastic tissue ; c, Delicate membrane of 
which the cell--\vall is constructed with elastic fibres attached to it (after 
K5lliker). 



STRUCTURE OF THE LUNOS. 



193 



than the vessels, which are, on an average, -r^'^^- of an 
inch in diameter. Between the atmospheric air in the 
cells and the blood in these vessels, nothing intervenes 
but the thin membranes of the cells and capillaries and 
the delicate epithelial lining of the former ; and the 
exposure of the blood to the air is the more complete, 
because the folds of membrane between contiguous cells, 
and often the spaces between the walls of the same, con- 
tain only a single layer of capillaries, both sides of which 
are thus at once exposed to the air. 

The cells situated nearest to the centre of the lung are 
smaller, and their networks of capillaries are closer than 
those nearer to the circumference, in adaptation to the 

Fvj. 61.* 




more ready supply of fresh air to the central than the 
peripheral portion of the lungs. The cells of adjacent 
lobules do not communicate ; and those of the same lobule, 
or proceeding from the same intercellular passage, do so 
as a general rule only near angles of bifurcation ; so that, 



* Fig. 61. Capillaiy net- work of the pulmonary blood-vessels in the 
liuinan lung (from Kolliker) ^°. 





194 EESriRATION. 

when any bronchial tube is closed or obstructed, the 
supply of air is lost for all the cells opening into it or its 
branches. 

Mechanism of Hespiration. 

For the proper understanding of the mechanism by 
which air enters and is expelled from the lungs, the follow- 
ing facts must be borne in mind : — 

The lungs form two distinct hollow bags (communicating 
with the exterior through the trachea and larynx), and are 
always closely in contact with the inner surface of the 
chest-walls, while their lower portions are closely in con- 
tact with the diaphragm, or muscular partition which 
separates the chest from the abdomen (figs. 3 1 and 65). The 
lungs follow all movements of the parts in contact with them ; 
and for the evident reason that the outer surface of the 
lung-bag not being exposed directly to atmospheric pres- 
sure, while the inner surface is so exposed, the pressure 
from within preserves the lungs in close contact with the 
parts surrounding them, and obliterates, practically, the 
pleural space, and must continue to do so, until from some 
cause or other — say from an opening for the admission of 
air through the chest-walls, the pressure on the outside of 
the lung equals or exceeds that on the interior. Any such 
artificial condition of things, however, need not here be 
considered. 

For the inspiration of air into the lungs it will be evi- 
dent from the foregoing facts, that all that is necessary is 
such a movement of the side-walls or floor of the chest, or 
of both, that the capacity of the interior shall be enlarged. 
By such increase of capacity there will be of course a 
diminution of the pressure of the air in the lungs, and a 
fresh quantity will enter through the larynx and trachea 
to equalise the pressure on the inside and outside of the 
chest. For the expiration of air, on the other hand, 
it is also evident, that, by an opposite movement which 



MECHANISM OF EESPIRATIOX. 195 

^hall contract tlie capacity of the chest, the pressure in the 
interior will be increased, and air will be expelled, until 
the pressures within and without the chest are again 
<equal. In both cases the air passes through the trachea 
and larynx, whether in entering or leaving the lungs, 
there being no other communication with the exterior, and 
the lung, for the reason before mentioned, remains under 
all the circumstances described, closely in contact with the 
walls and floor of the chest. To speak of expansion of the 
chest, is to speak also of expansion of the lung. 

"We have now to consider the means by which the chest- 
cavity is alternately enlarged and contracted for the en- 
trance and expulsion of atmospheric air ; or, in technical 
terms, for inspiration and expiration. 

Bespiratory Movements, 

The chest is a cavity filled by the lungs, heart, and large 
blood-vessels, etc., and closed everywhere against the en- 
trance of air except by the way of the larynx and trachea. 
It is bounded behind and at the sides by the spine and 
ribs, and in iront by the sternum and cartilages of the ribs. 
Its floor is formed mainly by the diaphragm. 

The immediate inner lining of all these parts is the 
outer or polished layer of the pleura; and this membrane 
also is stretched continuously across the top of the chest- 
cavity, and mainly forms its roof. 

The enlargement of the capacity of the chest in inspira- 
tion is a muscular act ; the muscles concerned in producing 
the effect being chiefly the diaphragm and the external 
intercostal muscles, with that part of the internal, inter- 
•costal which is between the cartilages of the ribs. These 
are assisted by the levatores costarum, the serratus posticus 
superior, and some others. 

The vertical diameter of the chest is increased by the 
contraction and consequent descent of the diaphragm, — 
the sides of the muscle descending most, and the central 



196 EESPIRATIOX. 

tendon remaining comparatively unmoved while the in- 
tercostal, and other muscles just mentioned, by acting at 
the same time, not only prevent the diaphragm during its- 
contraction from drawing in the sides of the chest, but 
increase the diameter of the chest in the lateral^ di rection , 
by elev ating the ribs ; that is to say, by rotating them, to 
I speak roughly, around an_axis passing through their 
\ ^^!?!!?5^ ^^^ spinal attachments, — somewhat after the 
\ fashion of raising the handle of a bucket (fig. 62). This 
is not all, however. Another efi'ect of the contraction of 
the intercostal muscles is to increase the antero-posterior 
Fig. 62. 




diameter of the chest, — by partially straightening out the- 
angle between the rib and its cartilage, and thus lengthen- 
ing the distance between its spinal and sternal attachments 
(fig. 62, a). In this way, at the same time that the ribs 
are raised, the sternum is pushed forward. This forward 
movement of the sternum, which is accompanied by a 
slight upward movement, is in part accomplished also by a 
raising of the anterior extremities of the rib cartilages, 
which of course, in any movement, carry the sternum with 
them. The differences in shape and direction of the upper 
and lower true ribs, and the more acute angles formed by 



RESPIRATORY MOVEMENTS. 



19; 



the junction of the latter with their cartilages, make the 
•effect much greater at the lower than at the upper part of 
-.the chest. ^^ "~ 



Fi(j. 64. t 





The expansion of tlie chest in inspiration presents some 



* Fig. 63 (after Hutchinson). The changes of the thoracic and 
abdominal walls of the male during respiration. The hack is supposed 
to he fixed in order to throw forward the respiratory movement as much 
as possible. The outer black continuous line in front represents the 
ordinary breathing movement: the anterior margin of it being the 
boundary of inspiration, the posterior margin the limit of expiration. 
The line is thicker over the abdomen, since the ordinary respiratory 
movement is chiefly abdominal : thin over the chest, for there is less 
movement over that region. The dotted line indicates the movement 
on deep insjuration, during which the sternum advances while the 
abdomen recedes. 

t Fig. 64 (after Hutchinson). The respirator} movement in the female. 
The lines indicate the same changes as in the last figure. The thickness 
of the continuous line over the sternum shows the larger extent of the 
ordinary breathing movement over that region in the female than in 
the male. 



iqS respiration. 

peculiarities in different persons and circumstances. In- 
young children, it is effected almost entirely by the dia- 
phragm, which being highly arched in expiration, becomes 
flatter as it contracts, and, descending, presses on the 
abdominal viscera, and pushes forward the front walls of 
the abdomen. The movement of the abdominal walls 
being here more manifest than that of any other part, it is 
usual to call this the ahdominal mode or type of respiration. 
In adult men, together with the descent of the diaphragm, 
and the pushing forward of the front wall of the abdomen, 
the lower part of the chest and the stemum are subject to 
a wide movement in inspiration. In women, the move- 
ment appears less extensive in the lower, and more so in 
the upper, part of the chest ; a mode of breathing to which 
a greater mobility of the first rib is adapted, and which 
may have for its object the provision of sufficient space for 
respiration when the lower part of the chest is encroached 
upon by the pregnant uterus. MM. Beau "and Maissiat 
call the former the inferior costal, and the latter the superior 
costal, type of respiration ; but the annexed diagrams wiU 
explain the difference better than the names will, for these 
imply a greater diversity than naturally exists in the 
modes of inspiration. 

From the enlargement produced in inspiration, the chest 
and lungs return in ordinary tranquil expiration, by their 
elasticity ; the force employed by the inspiratory muscles in 
distending the chest and overcoming the elastic resistance 
of the lungs and chest -walls, being returned as an expira- 
tory effort when the muscles are relaxed. This elastic 
recoil of the rib-cartilages, but also of the lungs them- 
selves, in consequence of the elastic tissue which they 
contain in considerable quantity, is sufficient, in ordinary 
quiet breathing, to expel air from the chest in the intervals 
of inspiration, and no muscular power is required. In all . 
voluntary expiratory efforts, however, as in speaking, 
singing, blowing, and the like, and in many involuntary 



ELASTIC EECOIL OF LUNGS AND CHEST. 1 99 

actions also, as sneezing, coughing, etc., something more 
than merely passive elastic power is of course necessary, 
and the proper expiratory muscles are brought into action. 
By far the chief of these are the abdominal muscles, which, 
by pressing on the viscera of the abdomen, push up the 
floor of the chest formed by the diaphragm, and by thus 
making pressure on the lungs, expel air from them through 
the trachea and larynx. All muscles, however, which de- ; 
press the ribs, must act also as muscles of expiration, and 1 
therefore we must conclude that the abdominal muscles are 
assisted in their action by the greater part of the internal 
intercostals, the triangularis sterni, the serratus posticus 
infer ior7 etc. When^byThe efforts of the expiratory muscles, 
the chest has been squeezed to less than its average dia- 
meter, it again, on relaxation of the muscles, returns to 
the normal dimensions by virtue of its elasticity. The 
construction of the chest-walls, therefore, admirably adapts 
them for recoiling against and resisting as well undue con- 
traction as undue dilatation. 

As before mentioned, the lungs, after distension in the 
act of inspiration, contract by virtue of the elastic tissue 
which is present in the bronchial tubes, on and between 
the air-cells, and in the investing pleura. But in the 
natural condition of the parts, they can never contract to 
the utmost, but are always more or less " on the stretch," 
being kept closely in contact with the inner surface of the 
walls of the chest by atmospheric pressure, able to act only 
on their interior, and can contract away from these only 
when, by some means or other, as by making an opening 
into the pleural cavity, or by the efi'usion of fluid there, the 
pressure on the exterior and interior of the lungs becomes 
equal. Thus, under ordinary circumstances, the degree of 
contraction or dilatation of the lungs is dependent on that 
of the boundary walls of the chest, the outer surface of the 
one being in close contact with the inner surface of the 
other, and obliged to follow it in all its movements. 



200 RESPIRATION. 

Bespiratory Rhythm. 

The acts of expansion and contraction of the chest, take 
up, under ordinary circumstances, a nearly equal time, and 
can scarcely be said to be separated from each other by an 
intei'vening pause. 

The act of inspiring air, however, especially in women 
and children, is a little shorter than that of expelling it, 
and there is commonly a very slight pause between the end 
of expiration and the beginning of the next inspiration. 
The respiratory rhythm may be thus expressed : — 

Inspiration .... 6 

Expiration . . . . 7 or 8 

A very slight pause. ] 

Respiratory Movements of the Glottis. 

During the action of the muscles which directly draw 
air into the chest, those which guard the opening through 
which it enters are not passive. In hurried breathing the 
instinctive dilatation of the nostrils is well seen, although 
under ordinary conditions it may not be noticeable. The 
opening at the upper part of the larynx, however, or rima 
glottidis (fig. 65), is dilated at each inspiration, for the 
more ready passage of air, and collapses somewhat at each 
expiration, its condition, therefore, corresponding during 
respiration with that of the walls of the chest. There is a 
further likeness between the two acts in that, under ordi- 
nary circumstances, the dilatation of the rima glottidis is a 
muscular act, and its contraction chiefly an elastic recoil ; 
although, under various conditions, to be hereafter men- 
tioned, there may be, in the contraction of the glottis, con- 
siderable muscular power exercised. 



QUANTITY OF AIR RESPIRED. 201 



Quantity of Air Respired. 

The quantity of air that is changed in the lungs in each 
act of ordinary tranquil breathing is variable, and is very 
difficult to estimate, because it is hardly possible to breathe 
naturally while, as in an experiment, one is attending to 
the process. Probably 30 to 35 cubic inches are a fair . 
average in the case of healthy young and middle-aged vy i/ i- 
men ; but Bourgery is perhaps right in saying that old (J^/^ ^ 
people, even in health, habitually breathe more deeply, 
and change in each respiration a larger quantity of air 
than younger persons do. j 

The total quantity of air which passes into and out of 
the lungs of an adult, at rest, in 24 hours, has been esti- 
mated by Dr. E. Smith at about 686,000 cubic inches. 
This quantity, however, is largely increased by exertion ; 
and the same observer has computed the average amount 
for a hard-working labourer in the same time, at 1,568,390 
oubic inches. 

The quantity which is habitually and almost uniformly 
changed in each act of breathing, is called by Mr. Hutchin- 
son breathing air. The quantity over and above this which 
a man can draw into the lungs in the deepest inspiration, 
he names complemental air : its amount is various, as will 
be presently shown. After ordinary expiration, such as 
that which expels the breathing air, a certain quantity of 
air remains in the lungs, which may be expelled by a 
forcible and deeper expiration: this he terms reserve air. 
But, even after the most violent expiratory effort, the 
lungs are not completely emptied; a certain quantity 
always remains in them, over which there is no voluntary 
•control, and which may be called residual air. Its amount 
depends in great measure on the absolute size of the chest, 
and has been variously estimated at from forty to two 
hundred and sixty cubic inches. 

The greatest respiratory capacity of the chest is indi- 



202 EESPIRATION. 

cated by the quantity of air whicli a person can expel from 
his lungs by a forcible expiration after the deepest inspi- 
ration that he can make. Mr. Hutchinson names this the 
vital capacity : it expresses the power which a person ha& 
of breathing in the emergencies of active exercise, violence, 
and disease; and in healthy men it varies according to- 
stature, iceight, and age. 

It is found by Mr. Hutchinson, from whom most of our 
A ^ information on this subject is derived, that at a tempera- 
' - -ture of 60° F., 225 cubic inches is the averate vital capacity_^ 
4 . Mtr V Jc of a healthy person, five feet seven inches in height. For 
every inch of height above this standard the capacity is- 
increased, on an average, by eight cubic inches; and for 
every inch below, it is diminished by the same amount. 
This relation of capacity to height is quite independent of 
the absolute capacity of the cavity of the chest; for the 
cubic contents of the chest do not always, or even gener- 
ally, increase with the stature of the body ; and a person 
of small absolute capacity of chest may have a large capacity 
of respiration, and vice versa. The capacity of respiration is 
determined only by the mobility of the walls of the chest ;. 
but why this mobility should increase in a definite ratio 
with the height of the body is yet unexplained, and must 
be difficult of solution, seeing that the height of the body 
is chiefly determined by that of the legs, and not by the 
height of the trunk or the depth of the chest. But the vast 
number of observations made by Mr. Hutchinson seem to- 
leave no doubt of the fact as stated above. 

The influence of xceight on the capacity of respiration is 
less manifest and considerable than that of height : and it 
is difficult to arrive at any definite conclusions on this 
point, because the natural average weight of a healthy 
man in relation to stature has not yet been determined. 
As a general statement, however, it may be said that the 
capacity of respiration is not affected by weights under 
161 pounds, or 11 J stones; but that, above this point, it 



QUAXTITY OF AIR EESPIRED. 20$ 

is diminished at tlie rate of one cubic inch, for every addi- 
tional pound up to 196 pounds, or 14 stones; so that, for 
example, while a man of five feet six inches, and weighing 
less than ii|- stones, should be able to expire 217 cubic 
inches, one of the same height, weighing 12 J stones, might 
expire only 203 cubic inches. 

By age, the capacity appears to be increased from about 
the fifteenth to the thirty-fifth year, at the rate of five 
cubic inches per year, from thirty-five to sixty-five it 
diminishes at the rate of about one and a-half cubic inch 
per year ; so that the capacity of respiration of a man of 
sixty years old would be about 30 cubic inches less than 
that of a man forty years old, of the same height and 
weight. 

Mr. Hutchinson's observations were made almost exclu- 
sively on men ; and his conclusions are, perhaps, true of 
them alone ; for womeii, according to Bourgery, have only 
half the capacity of breathing that men of the same age 
have. 

The number of respirations in a healthy adult person 
usually ranges from fourteenjo eighteen__per minute. | 

It is greater in infancy and childhood ; and of course 
varies much according to different circumstances, such as 
exercise or rest, health or disease, etc. Variations in the | 
number of respirations correspond ordinarily with similar 
variations in the pulsations of the heart. In health the 1 
proportion is about i to 4, or i to 5, and when the ' 
rapidity of the heart's action is increased, that of the chest 
movement is commonly increased also ; but not in every 
case in equal proportion. It happens occasionally in 
disease, especially of the lungs or air-passages, that the 
number of respiratory acts increases in quicker proportion 
than the beats of the pulse ; and, in other affections, much 
more commonly, that the number of the pulses is greater 
in proportion than that of the respirations. 

According to Mr. Hutchinson, the force with which the 



204 



RESriEATIOX. 



inspiratory muscles are capable of acting, is greatest in 
individuals of the height of from five feet seven inches to 
five feet eight inches, and will elevate a column of three 
inches of mercury. Above this height, the force decreases 
as the stature increases ; so that the average of men of six 
feet can elevate only about two and a half inches of mer- 
cury. The force manifested in the strongest expiratory 
acts is, on the average, one-third greater than that exer- 
cised in inspiration. But this difference is in great 
measure due to the power exerted by the elastic reaction of 
the walls of the chest ; and it is also much influenced by 
the disproportionate strength which the expiratory muscles 
attain, from their being called into use for other purposes 
than that of simple expiration. The force of the inspira- 
tory act is, therefore, better adapted than that of the 
expiratory for testing the muscular strength of the body. 

The following table expresses the result of numerous 
■experiments by Mr. Hutchinson on this subject, the instru- 
ment used to gauge the inspiratory and expiratory power 
being a hcomadynamometer (see p. t^^ to which was V /S''^ 
Attached a tube fitting the nostrils, and through which the 
inspiratory or expiratory effort was made : — 



Power of 


, 


Tower of 


Inspiratory ^Muscles. 


Expiratory Muscles. 


I "5 in. 


Weak 


2 -Gin. 


2-0 ,, 


Ordiiiaiy 


2-5 „ 


2'5 „ . 


. Strong 


3'5 ,. 


3'5 » 


. Very strong . 


4-5 „ 


4-5 „ • 


. lleniarkable 


5-8 „ 


5-5 V 


. Very remarkable . 


7"o ,, 


6-0 „ . 


. Extraordinary . 


8-5 „ 


7'o „ 


. Very extraordinary 


lo-o ,, 



Mr. Hutchinson remarks : — " Suppose a man to lift by 
his inspiratory muscles three inches of mercury, what 
muscular effort has he used ? The mere quantity of fluid 
lifted may be very inconsiderable (and as such I have 
found men wonder they could not elevate more), but not 



QUANTITY OF AIR RESPIRED. 205 

so the power exerted, when we recollect that hydrostatic 
law, which Mr. Bramah adopted to the construction of a 
very convenient press. To apply this law here, the 
diaphragm alone must act under such an effort, with a 
force equal to the weight of a column of mercury 3 inches 
in height, and whose base is commensurate to the area of 
the diaphragm. The area of the base of one of the chests 
now before the Society, is 57 square inches; therefore, had 
this man raised 3 inches of mercury by his inspiratory 
muscles, his diaphragm alone in this act must have 
opposed a resistance equal to more than 23 oz. on every 
inch of that muscle, and a total weight of more than 83 lbs. 
^loreover, the sides of his chest would resist a pressure from 
the atmosphere equal to the weight of a covering of mer- 
cury three inches in thickness, or more than 23 oz. on every 
inch surface, which, if we take at 318 square inches, the 
chest will be found resisting a pressure of 73 1 lbs. ; and 
allowing the elastic resistance of the ribs as i^ inch of 
mercury, this will bring the weight resisted by the chest 
as follows : — 

Diapliragni . . . . -83 lbs. 
Walls of the cliest . . • • 73 1 , , 
Elastic force . . . . . 232 ,, 

Total .... 1046 „ 

'' In round numbers it may be said, that the parietes 
of the thorax resisted looolbs, of atmospheric pressure, 
and that not counterbalanced, — to say nothing of the 
elastic power of the lungs, which co-operated with this 
pressure. 

" I would not venture at present to state exactly the 
distribution of muscular fibre over the thorax, which is 
called into action when resisting this 1046 lbs., but I think 
I am safe in stating that nine-tenths of the thoracic sur- 
face conspire to this act. 

'' What is here said of the muscular part of the chest 



206 RESPIRATIOX. 

resisting such, a force, must not be confounded with a former 
statement of * two-thirds being lifted by the inspiratory 
muscles, and one-third left dormant,' under a force equal 
to 301 lbs. In this case the 301 lbs. are lifted; in the 
other, nine-tenths of 1046 lbs. are said to be resisted. 

" The glass receiver of an air-pump may resist 15 lbs. on 
the square inch, yet it may be said to lift nothing. This 
question of the thoracic muscular force and resistance, and 
muscular distribution, is rendered complicate by the pre- 
sence of so much osseous matter entering into the composi- 
tion of the chest, which can scarcely be considered to act 
the same as muscle." 

The great force of the inspiratory efforts during apnoea 
was well shown in some of the experiments performed by 
the Medico- Chirurgical Society's Committee on Suspended 
Animation. On inserting a glass tube into the trachea of 
a dog, and immersing the other end of the tube in a vessel 
of mercury, the respiratory efforts during apnoea were so 
great as to draw the mercury four inches up the tube. 
The influence of the same force was shown in other expe- 
riments, in which the heads of animals were immersed 
both in mercury and in liquid plaster of Paris. In both 
cases the material was found, after death, to have been 
drawn up into all the bronchial tubes, filling the tissue of 
the lungs. 

Much of the force exerted in inspiration is employed in 
overcoming the resistance offered by the elasticity of the 
walls of the chest and of the lungs. Mr. Hutchinson esti- 
mated the amount of this elastic resistance, by observing 
the elevation of a column of mercury raised by the return 
of air forced, after death, into the lungs, in quantity equal 
to the known capacity of respiration during life ; and he 
calculated that, in a man capable of breathing 200 cubic 
inches of air, the muscular power expended upon the elas- 
ticity of the walls of the chest, in making the deepest 
inspiration, would be equal to the raising of at least 



VITAL CAPACITY. 20/ 

301 pounds avoirdupois. To this must be added about 
150 lbs. for the elastic resistance of the lungs themselves, 
so that the total force to be overcome by the muscles in 
the act of inspiring 200 cubic inches of air is more than 
450 lbs. 

In tranquil respiration, supposing the amount of breath- 
ing air [to be twenty cubic inches, the resistance of the 
walls of the chest would be equal to lifting more than 
100 pounds; and to this must be added about 70 pounds 
for the elasticity of the lungs. The elastic force overcome 
in ordinary inspiration must, therefore, be equal to about 
170 pounds. 

It is probable, that in the quiet ordinary respiration, 
Tvhich is performed without consciousness or effort of the 
wiU, the only forces engaged are those of the inspiratory 
muscles, and the elasticity of the walls of the chest and 
the lungs. It is not known under what circumstances the 
contractile power which the bronchial tubes possess, by 
means of their organic muscular fibres, is brought into 
action. It is possible, as Dr. R. Hall maintained, that 
it may exist in expiration ; but it is more likely that 
its chief purpose is to regulate and adaj^t^in some measure, 
the quantity of air admitted to the lungs, and to each part 
of them, according to the supply of blood. Another pur- [ 
pose probably served by the muscular fibres of the bron- I 
chial tubes is that of contracting upon and gradually ex- \ 
pelling collections of mucus, which may have accumulated 
within the tubes, and cannot be ejected by forced expiratory 
efforts, owing to collapse or other morbid conditions of 
the portion of lung proceeding from the obstructed tubes 
(Gairdner). 

The muscular action in the lungs, morbidly excited, is | 
j)robably the chief cause of the phenomena of spasmodic >: 
asthma. It may be demonstrated by galvanizing the lungs 
shortly after taking them from the body. Under such a 
stimulus, they contract so as to lift up water placed in a 



208 RESPIEATIOIs^ 

tube introduced into the trachea (C. J. B. Williams) ; and 
Yolkmann has shown that they may be made to contract by 
stimulating their nerves. He tied a glass tube, drawn 
fine at one end, into the trachea of a beheaded animal • 
and when the small end was turned to the flame of a 
candle, he galvanised the pneumogastric trunk. Eacli 
time he did so the flame was blown, and once it wa& 
blown out. 

The changes of the air in the lungs effected by these 
respiratory movements are assisted by the various con- 
ditions of the air itself. According to the law observed in 
the difi'usion of gases, the carbonic acid evolved in the air- 
cells will, independently of anj^ respiratory movement, 
tend to leave the lungs, by diffusing itself into the external 
air, where it exists in less proportion ; and according to 
the same law, the oxygen of the atmospheric air will tend 
of itself towards the air-cells in which its proportion is 
less than it is in the air in the bronchial tubes or in that 
external to the body. But for this tendency in the oxygen 
and carbonic acid to mix uniformly, within and without 
the lungs, the resei-ve and residual air would, probably, 
be very injuriously charged with carbonic acid ; for the 
respiratory movements alone are not enough to empty 
the air-cells, and perhaps expel only the air which lies 
in the larger bronchial tubes. Probably also the change 
is assisted by the different temperature of the air 
within and without the lungs; and by the action of tlie 
cilia on the mucous membrane of the bronchial tubes, 
the continual vibrations of which may serve to prevent 
the adhesion of the air to the moist surface of the mem- 
brane. 

Movement of Blood in the Fiespiratory Organs. 

To be exposed to the air thus alternately moved into and 
out of the air-cells and minute bronchial tubes, the blood is 
propelled from the riglit ventricle through the pulmonary 



CONTEACTIOX OF BRONCHI. 209 

capillaries in steady streams, and slowly enougli to permit 
every minute portion of it to be for a few seconds exposed 
to the air, with only the thin walls of the capillary vessels 
and air-cells intervening. The pulmonary circulation is 
of the simplest kind : for the pulmonary artery branches 
regularly ; its successive branches run in straight lines, 
and do not anastomose ; the capillary plexus is uniformly 
spread over the air-cells and intercellular passages; and 
the veins derived from it proceed in a course as simple and 
uniform as that of the arteries, their branches converging 
but not anastomosing. The veins have no valves, or onty 
small imperfect ones prolonged from their angles of junc- 
tion, and incapable of closing the orifice of either of the 
veins between which they are placed. The pulmonary cir- 
culation also is unaffected by changes of atmospheric 
pressure, and is not exposed to the influence of the pressure 
of muscles : the force by which it is accomplished, and the 
course of the blood are alike simple. 

The blood which is conveyed to the lungs by the pul- 
monary arteries is distributed to these organs to be purified 
and made fit for the nutrition of all other parts of the 
body. The capillaries of the pulmonary vessels are ar- 
ranged solely with reference to this object, and therefore 
can have but little to do with the nutrition of the lungs ; 
or at least, only of those portions of the lungs with which 
they are in intimate connection for another purpose. For 
the nutrition of the rest of the lungs, including the pleura, 
interlobular tissue, bronchial tubes and glands, and the 
walls of the larger blood vessels, a special supply of arterial 
blood is furnished through one or two bronchial arteries, 
the branches of which ramify in all these parts. The blood 
of the bronchial artery, when, having served for the nutri- 
tion of these parts, it has become venous, is carried partly 
into the branches of the bronchial vein, and thence to the 
right auricle, and partly into the small branches of the 
pulmonary artery, or, more directly, into the pulmonary 

p 



2IO EESPIEATIOX. 

capillaries, whence, being with the rest of the blood arte- 
rialized, it is carried to the pulmonary veins and left side 
of the heart. 

Changes of the Air in Respiration. 

By their contact in the lungs the composition of both air 
and blood is changed. The alterations of the former being 
manifest, simpler than those of the latter, and in some 
degree illustrative of them, may be considered first. 

The atmosphere we breathe has, in every situation in 
which it has been examined in its natural state, a nearly 
uniform composition. It is a mixture of oxygen, nitrogen, 
carbonic acid, and watery vapour, with, commonly, traces 
of other gases, as ammonia, sulphuretted hydrogen, etc. 
Of every lOO volumes of pure atmospheric air, 79 volumes 
(on an average) consist of nitrogen, the remaining 2 1 of 
oxygen. The proportion of carbonic acid is extremely 
small; I0,000 volumes of atmospheric air contain only 
about 4 or 5 of carbonic acid. 

The quantity of watery vapour varies greatly, according 
to the temperature and other circumstances, but the at- 
mosphere is never without some. In this country, the 
average quantity of watery vapour in the atmosphere is 
I '40 per cent. 

The changes produced by respiration on the atmospheric 
air are, that, i, it is warmed; 2, its carbonic acid is in- 
creased ; 3, its oxygen is diminished; 4, its watery vapour 
is increased ; 5, a minute amount of organic matter and of 
free ammonia is added to it. 

I. The expired air, heated by its contact with the in- 
terior of the lungs, is (at least in most climates) hotter 
than the inspired air. Its temperature varies between 97*^ 
and 99J°, the lower temperature being observed when 
the air has remained but a short time in the lungs, rather 
than when it is inhaled at a very low temperature ; for 
whatever the temperature when inhaled may be, the air 



CHANGES OF AIR IN EESPIRATION. 21 1 

nearly acquires that of the blood before it is expelled from 
the chest. 

2. The carbonic acid in respired air is always increased ; 
but the quantity exhaled in a given time is subject to 
change from various circumstances. From every volume 
of air inspired, about 4 J per cent, of oxygen are abstracted ; 
while a rather smaller quantity of carbonic acid is added 
in its place. It may be stated, as a general average 
deduced from the results of experiments by Valentin and 
Brunner, that, under ordinary circumstances, the quantity 
of carbonic acid exhaled into the air breathed by a healthy 
adult man amounts to 1 346 cubic inches, or about 636 
grains per hour. According to this estimate, which cor- 
responds very closely with the one furnished by Sir H. 
Davy, and does not widely differ from those obtained by 
Allen and Pepys, Lavoisier, and Dr. Ed. Smith, the weight 
of carbon excreted from the lungs is about 173 grains per 
hour, or rather more than 8 ounces in the course of twenty- 
four hours. Discrepancies in the results obtained by 
different experimenters may be due to the variations to 
which the exhalation of carbonic acid is liable in different 
circumstances ; for even in health the quantity varies accord- 
ing to age, sex, diversities in the respiratory movements, 
external temperature, the degree of purity of the respired 
air, and other circumstances. Each of these deserves a 
brief notice, because it affords evidence concerning either 
the sources of carbonic acid exhaled, or the mode in which 
it is separated from the blood. 

a. Influence of Age and Sex. — According to Andral and 
Gavarret the quantity of carbonic acid exhaled into the 
air breathed by males, regularly increases from eight to 
thirty years of age ; from thirty to forty it is stationary 
or diminishes a little ; from forty to fifty the diminution is 
greater ; and from fifty to extreme age it goes on diminish- 
ing, till it scarcely exceeds the quantity exhaled at ten 
years old. In females (in whom the quantity exhaled is 

p 2 



212 RESPIRATION. 

always less than in males of the same age) the same 
regular increase in quantity goes on from the eighth year 
to the age of puberty, when the quantity abruptly ceases 
to increase, and remains stationary so long as they con- 
tinue to menstruate. When, however, menstruation has 
ceased, either in advancing years or in pregnancy, or 
morbid amenorrhoea, the exhalation of carbonic acid again 
augments; but when menstruation ceases naturally, it 
soon decreases again at the same rate that it does in 
old men. 

b. Influence of Respiratory Movements. — According to 
Vierordt, the more quickly the movements of respiration 
are performed, the smaller is the proportionate quantity 
of carbonic acid contained in each volume of the expired 
air. Thus he found that, with six respirations per minute, 
the quantity of expired carbonic acid was 5*528 per cent. ; 
with twelve respirations, 4-262 per cent. ; with twenty- 
four, 3*355 ; with forty-eight, 2*984 ; and with ninety-six, 
2-662. Although, however, the proportionate quantity of 
carbonic acid is thus diminished during frequent respira- 
tion, yet the absolute amount exhaled into the air within 
a given time is increased thereby, owing to the larger 
quantity of air which is breathed in the time. This is 
the case, whether the respiration be voluntarily accelerated, 
or naturally increased in frequency, as it is after feeding, 
active exercise, etc. By diminishing the frequency, and 
increasing the depth of respiration, the per-centage pro 
portion of carbonic acid in the expired air is diminished ; 
being in the deepest respiration as much as I -97 per cent, 
less than in ordinary breathing. But for this proportionate 
diminution also, there is a full compensation in the greater 
total volume of air which is thus breathed. Finally, the 
last half of a volume of expired air contains more carbonic 
acid than the half first expired ; a circumstance which is 
explained by the one portion of air coming from the 
remote part of the lungs, where it has been in more 



INFLUEXCE OF TEMPERATUEE AND SEASO]Sr. 213 

immediate and prolonged contact with the blood than the 
other has, which comes chiefly from the larger bronchial 
tubes. 

c. Iiifiuence of external Temperature. — The observations 
made by Vierordt at various temperatures between 38° F. 
and 75° F. show, for warm-blooded animals, that within 
this range, every rise equal to 10° F. causes a diminution 
of about two cubic inches in the quantity of carbonic 
acid exhaled per minute. Letellier, from experiments 
performed on animals at much higher and lower tempera- 
tures than the above, also found that the higher the tempe- 
rature of the respired air (as far as 104° F.), the less is the 
amount of carbonic aid exhaled into it, whilst the nearer 
it approaches zero the more does the carbonic acid increase. 
The greatest quantity exhaled at the lower temperatures he 
found to be about twice as much as the smallest exhaled at 
the higher temperatures. 

d. Season of the Year. — Dr. Edward Smith has shown 
that the season of the year, independently of temperature, 
also materially influences the respiratory phenomena ; for 
with the same temperature, at different seasons, there is a 
great diversity in the amount of carbonic acid expired. 
According to his observations, spring is the season of the 
greatest, and autumn of the least activity of the respiratory 
and other functions. 

e. Purity of the Respired Air. — ^The average quantity of 
carbonic acid given out by the lungs constitutes about 4*48 
per cent, of the expired air ; but if the air which is breathed 
be previously impregnated with carbonic acid (as is the case 
when the same air is frequently respired), then the quantity 
of carbonic acid exhaled becomes much less. This is 
shown by the results of two experiments performed by 
Allen and Pepys. In one, in which fresh air was taken in 
at each respiration, thirty-two cubic inches of carbonic acid 
were exhaled in a minute ; whilst in the other, in which the 
same air was respired repeatedly, the quantity of carbonic 



214 EESPIRATIOX. 

acid emitted in tlie same time was only 9*5 cubic inches. 
They found also that, however often the same air may be 
respired, even if until it will no longer sustain life, it does 
not become charged with more than ten per cent, of carbonic 
acid. The necessity of a constant supply of fresh air, by 
means of ventilation, through rooms in which many persons 
are breathing together, or in which, from any other source, 
much carbonic acid is evolved, is thus rendered obvious ; 
for even when the air is not completely irrespirable, yet in 
the same proportion as it is already charged with carbonic 
acid, does the further extrication of that gas from the lungs 
suffer hindrance. 

/. Hyyrometric State of Atmosphere. — Lehmann's observa- 
tions have shown that the amount of carbonic acid exhaled 
is considerably influenced by the degree of moisture of the 
atmosphere, much more being given off when the air is 
moist than when it is dry. 

g. Period of the Day. — The period of day seems to exercise 
a slight influence on the amount of carbonic acid exhaled 
in a given time, though beyond the fact that the quantity 
exhaled is much less by night, we are scarcely yet in a posi- 
tion to state that variations in the amount exhaled occur at 
uniform periods of the day, independently of the influence 
of other circumstances. 

h. Food. — By the use of food the quantity is increased, 
whilst by fasting it is diminished : and, according to Reg- 
nault and Reiset, it is greater when animals are fed on fari- 
naceous food than when fed on meat. Spirituous drinks, 
especially when taken on an empty stomach, are generally 
believed to produce an immediate and marked diminution 
in the quantity of this gas exhaled. Recent observations 
by Dr. Edward Smith, however, furnish some singular re- 
sults on this subject. Dr. Smith found, for example, that 
the effects produced by spirituous drinks depend much on 
the kind of drink taken. Pure alcohol tended rather to 
increase than to lessen respiratory changes, and the amount. 



EFFECTS OF EXEECISE AND SLEEP. 21 5 

therefore, of carbonic acid expired : rum, ale, and porter, 
also sherry, had very similar effects. On the other hand, 
brandy, whisky and gin, particularly the latter, almost 
always lessened the respiratory changes, and consequently 
the amount of carbonic acid exhaled. 

i. Exercise and Sleep. — Bodily exercise, in moderation, in- 
creases the quantity to about one-third more than it is 
during rest : and for about an hour after exercise, the volume 
of the air expired in the minute is increased about 1 1 8 
cubic inches : and the quantity of carbonic acid about yS 
cubic inches per minute. Violent exercise, such as full 
labour on the treadwheel, still further increases, according 
to Dr. E. Smith, the amount of the acid exhaled. 

During sleep, on the other hand, there is a considerable 
diminution in the quantity of this gas evolved ; a result pro- 
bably in great measure dependent on the tranquillity of 
breathing : directly after walking, there is a great, though 
quickly transitory, increase in the amount exhaled. A 
larger quantity is exhaled when the barometer is low than 
when it is high. 

3. The Oxygen in respired Air is always less than in the 
same air before respiration, and its diminution is generally 
proportionate to the increase of the carbonic acid. The 
experiments of Valentin and Brunner seem to show, that, 
for every volume of carbonic acid exhaled into the air, 
I '1742 1 volumes of oxygen are absorbed from it: and 
that when the average quantity of carbonic acid, i.e., 1 346 
cubic inches, or 636 grains, is exhaled in the hour, the 
quantity of oxygen absorbed in the same time is 1 5 84 cubic 
inches or 542 grains. According to this estimate, there is 
more oxygen absorbed than is exhaled with carbon to form 
carbonic acid without change of volume ; and to this general 
conclusion, namely, that the volume of air expired in a 
given time is less than that of the air inspired (allowance 
being made for the expansion in being heated), and that 
the loss is due to a portion of oxygen absorbed and not 



2l6 EESPIRATIOX. 

returned in the exhaled carbonic acid, all observers agree, 
though as to the actual quantity of oxygen so absorbed 
they differ even widely. 

The quantity of oxygen that does not combine with the 
carbon given off in carbonic acid from the lungs, is probably 
disposed of in forming some of the carbonic acid and water 
given off from the skin, and in combining with sulphur and 
phosphorus to form part of the acids of the sulphates and 
phosphates excreted in the urine, and probably also, from 
the experiments of Dr. Bence Jones, with the nitrogen of 
the decomposing nitrogenous tissues. 

The quantity of oxygen consumed seems to vary much, 
not only in different individuals, but in the same individual 
at different periods ; thus it is considerably influenced by 
food, being greater in dogs when fed on farinaceous than 
on animal food, and much diminished during fasting, while 
it varies at different stages of digestion. Animals of small 
size consume a relatively much greater amount of oxygen 
than larger ones. The quantity of oxygen in the atmosphere 
surrounding animals, appears to have very little influence 
on the amount of this gas absorbed by them, for the quan- 
tity consumed is not greater even though an excess of 
oxygen be added to the atmosphere experimented with 
(Regnault and Reiset). 

The Nitrogen of the Atmosphere, in relation to the respira- 
tory process, is supposed to serve only mechanically, by 
diluting the oxygen, and moderating its action upon the 
system. This purpose, or the mode of expressing it, has 
been denied by Liebig, on the ground that if we suppose 
the nitrogen removed, the amount of oxygen in a given 
space would not be altered. But, although it be true that, 
if all the nitrogen of the atmosphere were removed and 
not replaced by any other gas, the oxygen might still 
extend over the whole space at present occupied by the 
mixture of which the atmosphere is composed; yet since, 
under ordinary circumstances, oxygen and nitrogen, when 



EXHALATION OF WATERY VAPOIJE. 217 

mixed together in the ratio of one volume to four, produce 
a mixture which occupies precisely five volumes, with all 
the properties of atmospheric air, it must result that a 
given volume of atmosphere drawn into the lungs con- 
tains four-fifths less weight of oxygen than an equal 
volume composed entirely of oxygen. The greater rapidity 
and brilliancy with which combustion goes on in an atmo- 
sphere of oxygen than in one of common air, and the 
increased rapidity with which the ordinary effects of 
respiration are produced when oxygen instead of atmo- 
spheric air is breathed, seem to leave no doubt that the 
nitrogen with which the oxygen of the atmosphere is 
mixed has the efiect of diluting this gas, in the same sense 
and degree as one part of alcohol is diluted when mixed 
with four parts of water. 

It has been often discussed whether nitrogen is ever 
absorbed by or exhaled from the lungs during respiration. 

At present, all that can be said on the subject is that, 
under most circumstances, animals appear to expire a very 
small quantity above that which exists in the inspired air. 
During prolonged fasting, on the contrary, a small quantity 
appears to be absorbed. 

4. Watery Vapour is, under ordinary circumstances, 
always exhaled from the lungs in breathing. The quan- 
tity emitted is, as a general rule, sufficient to saturate the 
expired air, or very nearly so. Its absolute amount is, 
therefore, influenced by the following circumstances. First, 
by the quantity of air respired ; for the greater this is, the 
greater also wiU be the quantity of moisture exhaled. 
Secondly, by the quantity of watery vapour contained in 
the air previous to its being inspired ; because the greater 
this is, the less will be the amount required to complete 
the saturation of the air. Thirdly, by the temperature of 
the expired air ; for the higher this is, the greater will be 
the quantity of watery vapour required to saturate the 
air. Fourthly, by the length of time which each volume 



2l8 RESPIEATIOK 

of inspired air is allowed to remain in the lungs ; for it 
seems probable that, although during ordinary respiration 
the expired air is always saturated with watery vapour, 
yet when respiration is performed very rapidly the air has 
scarcely time to be raised to the highest temperature, or be 
fully charged with moisture ere it is expelled. 

For ordinary cases, however, it may be held that the 
expired air is saturated with watery vapour, and hence is 
derivable a means of estimating the quantity exhaled in 
any given time ; namely, by subtracting the quantity con- 
tained in the air inspired from the quantity which (at the 
barometric pressure) would saturate the same air at the 
temperature of expiration, which is ordinarily about 99°. 
And, on the other hand, if the quantity of watery vapour 
in the expired air be estimated, the quantity of air itself 
may firom it be determined, being as much as that quantity 
of watery vapour would saturate at the ascertained tem- 
perature and barometric pressure. 

The quantity of water exhaled from the lungs in twenty- 
four hours ranges (according to the various modifying cir- 
cumstances already mentioned) from about 6 to 27 ounces, 
the ordinary quantity being about 9 or 10 ounces. Some 
of this is probably formed by the combination of the excess 
of oxygen absorbed in the lungs with the hydrogen of the 
blood ; but the far larger proportion of it must be the mere 
exhalation of the water of the blood, taking place from the 
surfaces of the air-passages and cells, as it does from the 
fi:ee surfaces of all moist animal membranes, particularly 
at the high temperature of warm-blooded animals. It is 
exhaled from the lungs whatever be the gas respired, con- 
tinuing to be expelled even in hydrogen gas. 

5. The Rev. J. B. Reads showed, some years ago, and 
Dr. Richardson's experiments confirm the fact, that am- 
monia is among the ordinary constituents of expired air. 
It seems probable, however, both from the fact that this 
substance cannot be always detected, and from its minute 



CHAXGES IX BLOOD. 219 

amount when present, that the whole of it may he derived 
from decomposing particles of food left in the mouth, or 
from carious teeth or the like ; and that it is, therefore, 
only an accidental constituent of expired air. 

The quantity of organic matter in the breath has been 
lately investigated by Dr. Ransome, who calculates that 
about 3 grains are given off from the lungs of an adult in 
twenty-four hours. 

Changes produced in the Blood by Respiration. 

The most obvious change which the blood undergoes in 
its passage through the lungs is that of colour, the dark 
crimson of venous blood being exchanged for the bright 
scarlet of arterial blood. (The circumstances which have 
been supposed to give rise to this change, the conditions 
capable of effecting it independent of respiration, and some 
other differences between arterial and venous blood, were 
discussed in the chapter on Blood, p. 85) : — 2nd, and in 
connection with the preceding change, it gains oxygen ; 
^rd, it loses carbonic acid; 4th, it becomes 1° or 2° F. 
warmer; ^th, ic coagulates sooner and more firmly, and, 
apparently, contains more fibrin. 

The oxygen absorbed into the blood from the atmospheric 
air in the lungs is combined chemically with the haemo- 
globin of the red blood corpuscles. In this condition it is 
carried in the arterial blood to the various parts of the 
body, and with it is, in the capillary system of vessels, 
brought into near relation or contact with the elementary 
parts of the tissUes. Herein co-operating probably in the 
process of nutrition, or in the removal of disintegrated 
parts of the tissues, a certain portion of the oxygen which 
the arterial blood contains disappears, and a proportionate 
quantity of carbonic acid and water is formed. 

But it is not alone in the disintegrating processes to 
which all parts of the body are liable, that oxygen is con- 
sumed and carbonic acid and water are formed in its 



220 RESPIRATIOX. 

consumption. A like process occurs in the "blood itself, 
independently of the decay of the tissues; for on the 
continuance of such chemical processes depend, directly 
or indirectly, not only the temperature of the body, but 
all the forces, the nervous, the muscular, and others, 
manifested by the living organism. 

The venous blood, containing the new-formed carbonic 
acid, returns to the lungs, where a portion of the carbonic 
acid is exhaled, and a fresh supply of oxygen is again 
taken in. 

Mechanism of Various Respiratory Actions. 

It will be well here, perhaps, to explain some respiratory 
acts, which appear at first sight somewhat complicated, 
but cease to be so when the mechanism by which they 
are performed is clearly understood. The accompanying 
diagram (fig. 65) shows that the cavity of the chest is 
separated from that of the abdomen by the diaphragm, 
which, when acting, will lessen its curve, and thus de- 
scending, will push downwards and forwards the abdominal 
viscera; while the abdominal muscles have the opposite 
effect, and in acting will push the viscera upwards and 
backward, and with them the diaphragm, supposing its 
ascent to be not from any cause interfered with. From 
the same diagram it will be seen that the lungs communi- 
cate with the exterior of the body through the glottis, and 
further on through the mouth and nostrils — through 
either of them separately, or through both at the same 
time, according to the position of the soft palate. The 
stomach communicates with the exterior of the body 
through the oesophagus, pharynx, and mouth; while 
below, the rectum opens at the anus, and the bladder 
through the urethra. All these openings, through which 
the hollow viscera communicate with the exterior of the 
body, are guarded by muscles, called sphincters, which can 



MECHANISM OF EESPIRATORY ACTIONS. 221 



act independently of each other. The position of the latter 
is indicated in the diagram. 

Let us take Fi^j. 65. 

first the simple 
act of sighing. 
In this case 
there is a rather 
prolonged in- 
spiratory effort 
by the dia- 
phragm and 
other muscles 
concerned in 
inspiration ; 
the air almost 
noiselessly pas- 
sing in through 
the glottis, and 
by the elastic 
recoil of the 
lungs and chest- 
walls, and pro- 
bably also of 
the abdominal 
walls, being 
rather suddenly 
expelled again. 

Now, in the first, or inspiratory part of this act, the 
descent of the diaphragm presses the abdominal viscera 
downwards, and of course this pressure tends to evacuate 
the contents of such as communicate with the exterior of 
the body. Inasmuch, however, as their various openings 
are guarded by sphincter muscles, in a state of constant 
tonic contraction, there is no escape of their contents, 
and air simply enters the lungs. In the second, or expira- 
tory part of the act of sighing, there is also pressure made 




222 EESPIRATIOX. • 

on the abdominal viscera in the opposite direction, by the 
elastic or muscular recoil of the abdominal walls ; but the 
pressure is relieved by the escape of air through the open 
glottis, and the relaxed diaphragm is pushed up again into 
its original position. The sphincters of the stomach, 
rectum, and bladder act as before. 

Hiccough resembles sighing in that it is an inspiratory 
act, but the inspiration is sudden instead of gradual, from 
the diaphragm acting suddenly and spasmodically ; and the 
air, therefore, suddenly rushing through the unprepared 
rima glottidis, causes vibration of the vocal cords, and the 
peculiar sound. 

In the act of coughing, there is most often first an in- 
spiration, and this is followed by an expiration ; but when 
the lungs have been filled by the preliminary inspiration, 
instead of the air being easily let out again through 
the glottis, the latter is momentarily closed by the 
approximation of the vocal cords ; and then the abdo- 
minal muscles, strongly acting, push up the viscera 
against the diaphragm, and thus make pressure on the 
air in the lungs until its tension is sufficient to burst 
open noisily the voeal cords which oppose its outward pas- 
sage. In this way a considerable force is exercised, and 
mucus or any other matter that may need expulsion jfrom 
the lungs or trachea is quickly and sharply expelled by 
the out-streaming current of air. 

Now it is evident on reference to the diagram (fig. 65 ), 
that pressure exercised by the abdominal muscles in the 
act of coughing, acts as forcibly on the abdominal viscera 
as on the lungs, inasmuch as the viscera form the medium 
by which the upward pressure on the diaphragm is made, 
and of necessity there is quite as great a tendency to the 
expulsion of their contents as of the air in the lungs. 
The instinctive and, if necessary, voluntarily increased 
contraction of the sphincters, however, prevents any 
escape at the openings guarded by them, and the pres- 



COUGHING; SNEEZING; VOMITING. 223 

sure is effective at one part only, namely, the rima 
glottidis. 

The same remarks that apply to coughing, are almost 
exactly applicable to the act of sneezing ; but in this in- 
stance the blast of air, on escaping from the lungs, is 
directed by an instinctive contraction of the pillars of the 
fauces and descent of the soft palate, chiefly through the 
nose, and any offending matter is thence expelled. 

In the act of vomiting, as in coughing, there is first an 
inspiration; the glottis is then closed, and immediately 
afterwards the abdominal muscles strongly act ; but here 
occurs the difference in the two actions. Instead of the 
vocal cords yielding to the action of the abdominal mus- 
cles, they remain tightly closed. Thus the diaphragm 
being unable to go up, forms an unyielding surface against 
which the stomach can be pressed. It is fixed, to use a 
technical phrase. At the same time the cardiac sphincter 
being relaxed while the pylorus is closed (see fig. 65), and 
the stomach itself also contracting, the action of the abdo- 
minal muscles, by these means assisted, expels the contents 
of the organ through the oesophagus, pharynx, and mouth. 
The reversed peristaltic action of the oesophagus probably 
increases the effect. 

In the act of voluntary expulsion of urine or faeces, 
there is first an inspiration, as in coughing, sneezing, and 
vomiting; the glottis is then closed, and the diaphragm fixed 
as in vomiting. Now, however, both the rima glottidis and 
the cardiac opening of the stomach remain closed, and the 
sphincter of the bladder or rectum, or of both, being re- 
laxed, the evacuation of the contents of these viscera takes 
place accordingly ; the effect being, of course, increased by 
the muscular and elastic contraction of their own walls. 
As before, there is as much tendency to the escape of 
the contents of the lungs or stomach as of the rectum or 
bladder ; but the pressure is relieved only at the orifice, 
the sphincter of which instinctively or involuntarily yields. 



224 EESPIRATION. 

In all these expulsive actions the diaphragm is quite 
passive; and when it is fixed^ it is in consequence of 
the closure of the glottis (which by preventing the exit of 
air from the lungs prevents its upward movement), not 
from any exertion on its own part. 

In females, during parturition, almost an exactly similar 
action occurs, so far as the diaphragm and abdominal 
walls are concerned, to that which takes place in a strain- 
ing effort at expulsion of urine or feeces. The contraction 
of the uterus, however, is both relatively and absolutely 
more powerful than that of the bladder or rectum, although 
it is greatly assisted by the inspiratory effort, by the fixing 
•of the diaphragm, and by the action of the abdominal 
muscles, as in the other acts just described. In parturi- 
tion, as in vomiting, the action of the abdominal muscles 
is, to a great extent, involuntary — more so than it com- 
monly is in the expulsion of faeces or urine ; but in these 
latter instances also, in cases of great pain and difficulty, 
it may cease to be a voluntary act, and be quite beyond 
the control of the will. 

In speaking, there is a voluntary expulsion of air through 
the glottis by means of the abdominal muscles ; and the 
vocal cords are put, by the muscles of the larynx, in a 
proper position and state of tension for vibrating as the 
air passes over them, and thus producing sound. The 
sound is moulded into words by the tongue, teeth, lips, 
etc. — the vocal cords producing the sound only, and having 
nothing to do with articulation. 

Singing Tesemhles speaking in the manner of its pro- 
duction ; the laryngeal muscles, by variously altering the 
position and degree of tension of the vocal cords, pro- 
ducing the different notes. Words used in the act of 
singing are of course framed, as in speaking, by the 
tongue, teeth, lips, etc. 

Sniffing is produced by a somewhat quick action of the 
diaphragm and other inspiratory muscles. The mouth is 



SNIFFING; SUCKING. 22$ 

however, closed, and by these means the whole stream of 
air is made to enter by the nostrils. The alto nasi are, 
commonly, at the same time, instinctively dilated. 

Suckinrj is not properly a respiratory act, but it may be 
most conveniently considered in this place. It is caused 
chiefly by the depressor muscles of the os hyoides. These, 
by drawing downwards and backwards the tongue and 
floor of the mouth, produce a partial vacuum in the latter ; 
and the weight of the atmosphere then acting on all sides 
tends to produce equilibrium on the inside and outside of 
the mouth as best it may. The communication between 
the mouth and pharynx is completely shut ofi", probably 
by the contraction of the pillars of the soft palate and 
descent of the latter so as to touch the back of the tongue ; 
and the equilibrium, therefore, can be restored only by the 
entrance of something through the mouth. The action, 
indeed, of the tongue and floor of the mouth in sucking 
may be compared to that of the piston in a syringe, and 
the muscles which pnll down the os hyoides and tongue, 
to the power which draws the handle. 

In the preceding account of respiratory actions, the 
diaphragm and abdominal muscles have been, as the chief 
muscles engaged and for the sake of clearness, almost alone 
referred to. But, of course, in all inspiratory actions, the 
other muscles of inspiration (p. 195) are also more or less 
engaged; and in expiration, the abdominal muscles are 
assisted by others, previously enumerated (p. 199) as 
grouped in action with them. 

Influence of the Nervous System in Uespiration, 

Like all other functions of the body, the discharge of 
which is necessary to life, respiration must be essentially 
an involuntary act. Else, life would be in constant danger, 
and would cease on the loss of consciousness for a few 
moments, even in sleep. But it is also necessary that 
respiration should be to some extent under the control of 

Q 



226 RESriRATIOX. 

the will. For were it not so, it would be impossible to 
perform those voluntary respiratory acts which have been 
just enumerated and explained, as speaking, singing, 
straining, and the like. 

The respiratory movements and their regular rhythm, 
so far as they are involuntary and independent of con- 
sciousness (as on all ordinary occasions they are), seem to 
be under the absolute governance of the medulla oblon- 
gata, which, as a nervous centre, receives the impression 
of the *' necessity of breathing," and reflects it to the 
phrenic and such other motor nerves as will bring into 
co-ordinate and adapted action the muscles necessary to 
inspiration. 

In the cases of voluntary respiratory acts, we may 
believe that the brain, as well as the medulla oblongata, 
is engaged in the process ; for we have no evidence of the 
mind exercising either perception or will through any 
other organ than the brain. But even when the brain 
is thus in action, it appears to be the medulla oblongata 
which combines the several respiratory muscles to act 
together. In such acts, for example as those of cough- 
ing and sneezing, the mind first perceives the irritation at 
the larynx or nose, and may exercise a certain degree of 
will in determining the actions, as e.g., in the taking of 
the deep inspiration which always precedes them. But the 
mode in which the acts are performed, and the combi- 
nation of muscles to effect them, are determined by tlie- 
medulla oblongata, independently' of the will, and have 
the peculiar character of reflex involuntary movements, in 
being always, and without practice or experience, precisely^ 
adapted to the end or purpose. 

In these, and in all the other extraordinary respiratory 
actions, such as are seen in dj'spncea, or in straining, 
yawning, hiccough, and others, the medulla oblongata 
brings into adapted combination of action many other 
muscles besides those commonly exerted in respiration.. 



INFLUENCE OF NERVOUS SYSTEM. 



227 



Almost all the muscles of the body, in violent efforts of 
dyspnoea, coughing, and the like, may be brought into 
action at once, or in quick succession ; but more particu- 
larly the muscles of the larynx, face, scapula, spine, and 
abdomen co-operate in these efforts with the muscles of the 
chest. These, therefore, are often classed as secondary 
muscles of respiration; and the nerves supplying them, 
including especially the facial pneumogastric, spinal, 
accessory, and external respiratory nerves, were classed 
by Sir Charles Bell with the phrenic, as the respiratory 
system of nerves. There appears, however, no propriety in 
making a separate system of these nerves, since their mode 
of action is not peculiar, and many besides them co- 
operate in the respiratory acts. That which is peculiar 
in the nervous influence, directing the extraordinary move- 
ments of respiration, is, that so many nerves are com- 
bined towards one purpose by the power of a distinct 
nervous centre, the medulla oblongata. In other than 
respiratory movements, these nerves may act singly or 
together, without the medulla oblongata; but after it is 
destroyed, no movement adapted to respiration can be per- 
formed by any of the muscles, even though the part of the 
spinal cord from which they arise be perfect. The phrenic 
nerves, for example, are unable to excite respiratory move- 
ment of the diaphragm when their connection with the 
medulla oblongata is cut off, though their connection with 
the spinal cord may be uninjured.* 

Effects of the Suspension and Arrest of Respiration. 

These deserve some consideration, because of the illustra- 
tion which they afford of the nature of the normal processes 
of respiration and circulation. When the process of respi- 
ration is stopped, either by arresting the respiratory move- 

* The influence of tlie nervous system in respiration will be again 
and more particularly considered in tlie section treating of the medulla 
oblongata and pneumogastric nerves. 

Q 2 



228 EESPIRATION. 

ments, or permitting them to continue in an atmosphere 
deprived of uncombined oxygen, the circulation of blood 
through the lungs is retarded, and at length stopped. The 
immediate effect of such retarded circulation is an obstruc- 
tion to the exit of blood from the right ventricle : this is 
followed by delay in the re'turn of venous blood to the heart ; 
and to this succeeds venous congestion of the nervous centres 
and all the other organs of the body. In such retardation, 
also, an unusually small supply of blood is transmitted 
through the lungs to the left side of the heart ; and this 
small quantity is venous. 

The condition, then, in which a suffocated, or asphyxi- 
ated animal dies is, commonly, that the left side of the 
heart is nearly empty, while the lungs, right side of the 
heart, and other organs, are gorged wath venous blood. 
To this condition many things contribute. 1st. The ob- 
structed passage of blood through the lungs, which appears 
to be the first of the events leading to suffocation, seems 
to depend on the cessation of the interchange of gases, as 
if blood charged with carbonic acid could not pass freely 
through the pulmonary capillaries. But the stagnation of 
blood in the pulmonary capillaries would not, perhaps, be 
enough to stop entirely the circulation, unless the action 
of the heart were also weakened. Therefore, 2ndly, the 
fatal result is probably due, in some measure, to the 
enfeebled action of the right side of the heart, in conse- 
quence of its over "distension by blood continually flowing 
into it ; this flow, probably, being much increased by the 
powerful but fruitless efforts continually made at inspira- 
tion (Eccles). And 2'^'dbj, because of the obstruction at the 
right side of the heart, there must be venous congestion in 
the medulla oblongata and nervous centres : and this evil 
is augmented by the left ventricle receiving and propelling 
none but venous blood. Hence, slowness and disorder of the 
respiratory movements and of the movements of the heart 
may be added. Under all these conditions combined, the 



SUSPENDED ANIMATION. 229 

heart at length ceases to act ; the cessation of its action 
being also in great measure, probably, brought about, 4thli/, 
by the imperfect supply of oxygenated blood to its muscular 
tissue. 

In some experiments performed by a committee ap- 
pointed by the Medico-Chirurgical Society to investigate 
the subject of Suspended Animation, it was found that, in 
the dog, during simple apncea, i.e., simple privation of air, 
as by plugging the trachea, the average duration of the 
respiratory movements after the animal had been deprived 
of air, was 4 minutes 5 seconds; the extremes being 
3 minutes 30 seconds, and 4 minutes 40 seconds. The 
average duration of the heart's action, on the other hand, 
was 7 minutes 1 1 seconds ; the extremes being 6 minutes 
40 seconds, and 7 minutes 45 seconds. It would seem, 
therefore, that on an average, the heart's action continues 
for 3 minutes 15 seconds after the animal has ceased to 
make respiratory efforts. A very similar relation was ob- 
served in the rabbit. Recovery never took place after the 
heart's action had ceased. 

The res alts obtained by the committee on the subject of 
drowning were very remarkable, especially in this respect, 
that whereas an animal may recover, after simple depriva- 
tion of air for nearly four minutes, yet, after submersion in 
water for i^ minutes, recovery seems to be impossible. 
This remarkable difference was found to be due, not to the 
mere submersion, nor directly to the struggles of the 
animal, nor to depression of temperature, but to the two 
facts, that in drowning, a free passage is allowed to air out 
of the lungs, and a free entrance of water into them. In 
proof of the correctness of this explanation it was found 
that when two dogs of the same size, one, however, having 
his windpipe plugged, the other not, were submerged at 
the same moment, and taken out after being under water 
for 2 minutes, the former recovered on removal of the plug, 
the latter did not. It is probably to the entrance of water 



2 so EESPIRATIOX. 

into the lungs that the speedy death in drowning is mainly- 
due. The results o^ post-mortem examination strongly sup- 
port this view. On examining the lungs of animals deprived 
of air by plugging the trachea, they were found simply 
congested ; but in the animals drowned, not only was the 
congestion much more intense, accompanied with ecchy- 
mosed points on the surface and in the substance of the 
lung, but the air tubes were completely choked up with 
a sanious foam, consisting of blood, water, and mucus, 
churned up with the air in the lungs by the respiratory 
efforts of the animal. The lung-substance, too, appeared 
to be saturated and sodden with water, which, stained 
slightly with blood, poured out at any point where a section 
was made. The lung thus sodden with water was heavy 
(though it floated), doughy, pitted on pressure, and was 
incapable of collapsing. It is not difficult to understand 
how, by such infarction of the tubes, air is debarred 
from reaching the pulmonary cells : indeed the inability 
of the lungs to collapse on opening the chest is a proof 
of the obstruction which the froth occupying the air-tubes 
offers to the transit of air. The entire dependence of the 
early fatal issue, in apnoea by drowning, upon the open 
condition of the windpipe, and its results, was also 
strikingly shown by the following experiment. A strong 
dog had its windpipe plugged, and was then submerged in 
water for four minutes ; in three-quarters of a minute after 
its release it began to breathe, and in four minutes had fully 
recovered. This experiment was repeated with similar results 
on other dogs. When the entrance of water into the lungs, 
and its drawing up with the air into the bronchial tubes by 
means of the respiratory efforts, were diminished, as by 
rendering the animal insensible by chloroform previously 
to immersion, and thus depriving it of the power of making 
violent respiratory efforts, it was found that it could bear 
immersion for a longer period without dying than when not 
thus rendered insensible. Probably to a like diminution 



ANIMAL HEAT. 23 I 

in the respiratory efforts, may also be ascribed the 
greater length of time persons have been found to bear 
submersion without being killed, when in a state of in- 
toxication, poisoning by narcotics, or during insensibility 
fi-om syncope. 

It is to the accumulation of carbonic acid in the blood, 
-and its conveyance into the organs, that we must, in the 
first place, ascribe the phenomena of asphyxia. For when 
this does not happen, all the other conditions may exist 
without injury ; as they do, for example, in hybernating 
warm-blooded animals. In these, life is supported for 
many months in atmospheres in which the same animals, 
in their full activity, would be speedily suffocated. During 
the periods of complete torpor, their respiration almost 
entirely ceases ; the heart acts very slowly and feebly ; the 
processes of organic life are all but suspended, and the 
animal may be with impunity completely deprived of atmo- 
spheric air for a considerable period. Spallanzani kept a 
marmot, in this torpid state, immersed for four hours in 
carbonic acid gas, without its suffering any apparent in- 
€onvenienc3 Dr. Marshall Hall kept a lethargic bat under 
water for 16 minutes, and a lethargic hedgehog for 22 J 
minutes ; and neither of the animals appeared injured by 
the experiment. 



CHAPTER VIII. 



ANIMAL HEAT. 



The average temperature of the human body in those 
internal parts which are most easily accessible, as the mouth 
and rectum, is from 98*5° to 99*5° F. 

In different parts of the external surface of the human 
body the temperature varies only to the extent of two or 
three degrees, when all are alike protected from cooling 



232 ANIMAL HEAT. 

influences ; and the difference which under these circum- 
stances exists, depends chiefly upon the difierent degrees of 
blood-supply. In the arm-pit — the most convenient situa- 
tion, under ordinary circumstances, for examination by the 
thermometer — the average temperature is 98 "6° F. 

The chief circumstances by which the temperature of the 
healthy body is influenced are the following : — 

Afje. — The average temperature of the new-born child is 
only about 1° F. above that proper to the adult ; and the 
difference becomes still more trifling during infancy and 
early childhood. According to Wunderlich, the temperature 
falls to the extent of about -1° to J° F. from early infancy 
to puberty, and by about the same amount from puberty to 
fifty or sixty years of age. In old age the temperature- 
again rises, and approaches that of infancy. 

Although the average temperature of the body, however, 
is not lower than that of younger persons, yet the power of 
resisting cold is less in them — exposure to a low temperature 
causing a greater reduction of heat than in young persons. 

The same rapid diminution of temperature was observed 
by M. Edwards in the new-bom young of most carnivorous 
and rodent animals when they were removed from the 
parent, the temperature of the atmosphere being between 
50° and 53j° F. ; whereas, while lying close to the body of 
the mother, their temperature was only 2 or 3 degrees 
lower than hers. The same law applies to the young of 
birds. Young sparrows, a week after they were hatched, 
had a temperature of 95° to 97°, while in the nest; but 
when taken from it, their temperature fell in one hour to 
66J°, the temperature of the atmosphere being at the time 
62 J°. It appears from his investigations, that in respect 
of the power of generating heat, some Mammalia are born 
in a less developed condition than others ; and that the 
young of dogs, cats, and rabbits, for example, are inferior 
to the young of those animals which are not bom blind.. 
The need of external warmth to keep up the temperature 



TEMPEEATCJRE OF THE EODY. 233 

of new-born children is well known ; the researches of M. 
Edwards show, that the want of it is, as Hunter suggested, 
a much more frequent cause of death in new-born children 
than is generally supposed, and furnish a strong argument 
against the idea, that children, by early exposure to cold, 
can soon be hardened into resisting its injurious influence. 

Sex. — The average temperature of the female would 
appear from observations by Dr. Ogle to be very slightly 
higher than that of the male. 

Period of the Day. The temperature undergoes a gradual 
alteration, to the extent of about i^ to ij° F. in the course 
of the day and night ; the minimum being at night or in 
the early morning, the maximum late in the afternoon. 

Exercise. — Active exercise raises the temperature of the 
body. This may be partly ascribed to the fact, that every 
muscular contraction is attended by the development of one 
or two degrees of heat in the acting muscle ; and that the 
heat is increased according to the number and rapidity of 
these contractions, and is quickly diffused by the blood 
circulating from the heated muscles. Possibly, also, some 
heat may be generated in the various movements, stretch- 
ings, and recoilings of the other tissues, as the arteries, 
whose elastic walls, alternately dilated and contracted, may 
give out some heat, just as caoutchouc alternately stretched 
and recoiling becomes hot. But the heat thus developed 
cannot be great. 

Moreover, the increase of temperature throughout th& 
whole body, produced by active exercise, is but small ; the 
great apparent increase of heat depending, in a great 
measure, on the increased circulation and quantity of blood, 
and, therefore, greater heat, in parts of the body (as the 
skin, and especially the skin of the extremities), which, at 
the same time that they feel more acutely than others any 
changes of temperature are, under ordinary conditions, by 
some degrees colder than organs more centrally situated. 

That the increased temperature of the skin during 



234 ANIMAL HEAT. 

exercise is not accompanied by a proportional increase of 
the heat of other parts, which are naturally much warmer, 
is well shown by some observations of Dr. J. Davy. 

Climate and Season. — In passing from a temperate to a 
hot climate the temperature of the human body rises 
slightly, the increase rarely exceeding 2° to .3° F. In 
summer the temperature of the body is a little higher than 
in winter ; the difference amounting to from 4-° to J° F. 
{Wunderlich). 

The same effects are observable in alterations of tem- 
perature not depending on season or climate. 

Food and Drink. — The effect of a meal upon the tempera- 
ture of a body is but small. A very slight rise usually occurs. 

Cold alcoholic drinks depress the temperature somewhat 
.(J° to 1° F.). Warm alcoholic drinks, as well as warm tea 
and coffee, raise the temperature (about J° F.). 

In disease the temperature of the body deviates from the 
normal standard to a greater extent than would be antici- 
pated from the slight effect of external conditions during 
health. Thus, in some diseases, as pneumonia and typhus, 
it occasionally rises as high as 106° or 107° F. ; and con- 
siderably higher temperatures have been noted. In a case 
of malignant fever recently recorded by Mr. Norman Moore, 
the temperature in the axilla rapidly rose to 1 1 1° F. ; when 
the patient died. The highest temperature recorded in a 
living man, 112*5° F., was observed by Wunderlich, in a 
case of idiopathic tetanus, at the time of death. In the 
morbus carideus, in which there is defective arterialization 
of the blood from malformation of the heart, the tem- 
perature of the body may be as low as 79° or ^y^ ; in 
Asiatic cholera a thermometer placed in the mouth some- 
time rises only to 77°or 79° ; and in a case of tubercular 
meningitis, observed by Dr. Gee, the temperature of the 
rectum remained for hours at 79*4° F. 

The temperature maintained by Mammalia in an active 
state of life, according to the tables of Tiedemann and 



FOOD AND DRIXK. 



235 



Rudolphi, averages I0I°. The extremes recorded by them 
were 96° and 106°, the former in the narwhal, the latter in 
a bat (Vespertilio Pipistrella). In birds, the average is as 
high as 107° ; the highest temperature, 111-25°, being in 
the small species, the linnets, etc. Among reptiles, Dr. 
John Davy found, that while the medium they were in was 
75°, their average temperature was 82*5 °. As a general 
rule, their temperature, though it falls with that of the 
surrounding medium, is, in temperate media, two or 
more degrees higher ; and though it rises also with that of 
the medium, yet at very high degrees it ceases to do so, 
and remains even lower than that of the medium. Fish 
and Invertebrata present, as a general rule, the same tem- 
perature as the medium in which they live, whether that 
be high or low ; only among fish, the tunny tribe, witli 
strong hearts and red meat-like muscles, and more blood 
than the average of fish have, are generally 7° warmer 
than the water around them. 

The difference, therefore, between what are commonly 
called the warm- and the cold-blooded animals, is not one 
of absolutely higher or lower temperature ; for the animals 
which to us, in a temperate climate, feel cold (being like 
the air or water, colder than the surface of our bodies), 
would, in an external temperature of 1 00°, have nearly the 
same temperature and feel hot to us. The real difference 
is, as Mr. Hunter expressed it, that what we call warm- 
blooded animals (birds and Mammalia), have a certain 
" permanent heat in all atmospheres," while the tempera- 
ture of the others, which we call cold-blooded, is " variable 
with every atmosphere." 

The power of maintaining a uniform temperature, which 
Mammalia and birds possess, is combined with the want of 
power to endure such changes of temperature of their bodies 
as are harmless to the other classes ; and when their power 
of resisting change of temperature ceases, they suffer serious 
disturbances or die. 



236 ANIMAL HEAT. 



Sources and Mode of Production of Heat in the Body. 

In explaining tlie chemical changes effected in the pro- 
cess of respiration (p. 219), it was stated that the oxygen 
of the atmosphere taken into the blood is combined, in the 
course of the circulation, with the carbon and the hydrogen 
of disintegrated and absorbed tissues, and of certain ele- 
ments of food which have not been converted into tissues. 
That such a combination between the oxygen of the atmo- 
sphere and the carbon and hydrogen in the blood, is con- 
tinually taking place, is made certain by the fact, that a 
larger amount of carbon and hydrogen is constantly being 
added to the blood from the food than is required for the 
ordinary purposes of nutrition, and that a quantity of 
oxygen is also constantly being absorbed from the air in 
the lungs, of the disposal of which no account can be given 
except by regarding it as combining, for the most part, 
"with the excess of carbon and hydrogen, and being excretefl 
in the form of carbonic acid and water. In other words^ 
the blood of warm-blooded animals appears to be always 
receiving from the digestive canal and the lungs more 
carbon, hydrogen, and oxygen than are consumed in the 
repair of the tissues, and to be always emitting carbonic 
acid and water, for which there is no other known source 
than the combination of these elements^' By such com- 
bination, heat is continually produced in the animal body. 
The same amount of heat will be evolved in the union of 
any given quantities of carbon and oxygen, and of hydrogen 
and oxygen, whether the combination be rapid and evident, 
as in ordinary combustion, or slow and imperceptible, as in 
the changes which occur in the living body. And since 
the heat thus arising will be generated wherever the blood 

* Some heat will also be generated in the combination of sulphm- and 
phosphorus -with oxygen, to which reference has been made (p. 216) ; 
but the amount thus produced is but smalh 



PRODUCTIOX OF HEAT. 



237 



is carried, every part of the body will be heated equally, or 
nearly so. 

This theory, that the maintenance of the temperature of 
the living body depends on continual chemical change, chiefly 
by oxidation, of combustible materials existing in the tissues 
and in the blood, has long been established by the demon- 
stration that the quantity of carbon and hydrogen which, 
in a given time, unites in the body with oxygen, is suffi- 
cient to account for the amount of heat generated in the 
animal within the same time : an amount capable of main- 
taining the temperature of the body at from 98° to I00°, 
notwithstanding a large loss by radiation and evaporation. 

Many things observed in the economy and habits of 
animals are explicable by this theory, and may here briefly 
be quoted, although no longer required as additional 
evidence for its truth. Thus, as a general rule, in the 
various classes of animals, as well as in individual ex- 
amples of each class, the quantity of heat generated in 
the body is in direct proportion to the activity of the 
respiratory process. The highest animal temperature, fon 
example, is :^ound in birds, in whom the function of 
respiration is most actively performed. In ^Mammalia, the 
process of. respiration is less active, and the average tem- 
perature of the body less, than in birds. In reptiles, both 
the respiration and the heat are at a much lower standard ; 
while in animals below them, in which the function of 
respiration is at the lowest point, a power of producing 
heat is, in ordinary circumstances, hardly discernible. 
Among these lower animals, however, the observations of 
Mr. Newport supply confirmatory evidence. He shows 
that the larva, in which the respiratory organs are smaller 
in comparison with the size of the body, has a lower tem- 
perature than the perfect insect. Volant insects have the 
highest temperature, and they have always the largest 
respiratory organs and breathe the greatest quantity of air ; 
while among terrestrial insects, those also produce the most 



238 ANIMAL HEAT. 

heat which have the largest respiratory organs and breathe 
the most air. During sleep, hybernation, and other states 
of inaction, respiration is slower or suspended, and the 
temperature is proportionately diminished ; while, on the 
other hand, when the insect is most active and respiring 
most voluminously, its amount of temperature is at its 
maximum, and corresponds with the quantity of respi- 
ration. Neither the rapidity of the circulation, nor the 
size of the nervous system, according to Mr. Newport, 
presents such a constant relation to the evolution of heat. 

On the Regulation of the Temperature of the Human Bodij. 

The continual production of heat in the body has been 
already referred to. There is also, of necessity, a continual 
loss. But in healthy warm-blooded animals, as already 
remarked, the loss and gain of heat are so nearly balanced 
one by the other, that under all ordinary circumstances, 
an uniform temperature, within two or three degrees, is- 
preserved. 

The loss of heat from the human body takes place chiefly 
by radiation and conduction from its surface, and by means^ 
of the constant evaporation of water from the same part,, 
and from the air-passages. In each act of respiration, 
heat is also lost by so much warmth as the expired air 
acquires (p. 2io). All food and drink which enter the 
body at a lower temperature than itself, abstract a small 
measure of heat, and the urine and faeces take about a like 
amount away, when they leave the body. Lastly, some 
part of the heat of the body is rendered imperceptible, and 
therefore lost as heat, by being manifested in the form of 
mechanical motion. 

By far the most important loss of heat from the body, — 
probably 80 or 90 per cent, of the whole amount, is that 
which proceeds from radiation, conduction, and evapora- 
tion from the skin. And it is to this part especially, and 
in a smaller measure to the air-passages, that we must look 



EEGTJLATION OF THE TEMPERATURE. 239 

for tlie means by whicli the temperature is regulated ; in 
other words, by which it is prevented from rising beyond 
the normal point on the one hand, or sinking below it on 
the other. The chief indirect means for accomplishing the 
same end are, variations in the amount and quality of the 
food and drink taken, variations in clothing, and in 
exposure to external heat or cold. 

In order to understand the means by which the heat of 
the body is regulated, it is necessary to take into consi- 
deration the following facts : First, the immediate source 
of heat in the body is the presence of a large quantity of 
a warm fluid — the blood, the temperature of which is, in 
health, about 100° F. In the second place, the blood,, 
while constantly moving in a multitude of different streams, 
is, every minute or so, gathered up in the heart into one 
large stream, before being again dispersed to all parts of 
the body. In this way, the temperature of the blood 
remains almost exactly the same in all parts ; for while a 
portion of it in passing through one organ, as the skin, 
may become cooler, and through another organ, as the 
liver, may become warmer, the effect on each separate 
stream is more or less neutralized when it mingles with 
another, and an average is struck, so to speak, for all the- 
streams when they form one, in passing through the 
heart. 

The means by which the skin is able to act as one of 
the most important organs for regulating the temperature 
of the blood, are — (i), that it offers a large surface for 
radiation, conduction, and evaporation ; (2), that it con- 
tains a large amount of blood ; (3), that the quantity of 
blood contained in it is the greater under those circum- 
stances which demand a loss of heat from the body, and 
vice versa. For the circumstance which directly determines 
the quantity of blood in the skin, is that which governs 
the supply of blood to aU the tissues and organs of the 
body, namely, the power of the vaso-motor nerves to cause 



240 ANIMAL HEAT. 

a greater or less tension of tlie muscular element in the 
walls of the arteries (see p. 141), and, in correspondence 
with this, a lessening or increase of the calibre of the vessel 
accompanied by a less or greater current of blood. A 
warm or hot atmosphere so acts on the nerve fibres of the 
skin, as to lead them to cause in turn a relaxation of the 
muscular fibre of the blood-vessels ; and, as a result, the 
skin becomes full-blooded, hot, and sweating ; and much 
heat is lost. With a low temperature, on the other hand, 
the blood-vessels shrink, and in accordance with the con- 
sequently diminished blood-supply, the skin becomes pale, 
and cold, and dry. Thus, by means of a self-regulating 
apparatus, the skin becomes the most important of the 
means by which the temperature of the body is regulated. 

In connection with loss of heat by the skin, reference 
has been made to that which occurs both by radiation 
and conduction, and by evaporation; and the subject of 
animal heat has been considered almost solely with regard 
to the ordinary case of man living in a medium colder than 
his body, and therefore losing heat in all the ways men- 
tioned. The importance of the means, however, adopted, 
so to speak, by the skin for regulating the temperature of 
the body, will depend on the conditions by which it is sur- 
rounded; an inverse proportion existing in most cases 
between the loss by radiation and conduction on the one 
hand, and by evaporation on the other. Indeed, the small 
loss of heat by evaporation in cold climates may go far to 
compensate for the greater loss by radiation ; as, on the 
other hand, the great amount of fluid evaporated in hot 
air may remove nearly as much heat as is commonly lost 
by both radiation and evaporation in ordinary tempera- 
tures ; and thus, it is possible, that the quantities of heat 
required for the maintenance of an uniform proper tem- 
perature in various climates and seasons are not so different 
as they, at first thought, seem. 

Many examples might be given of the power which the 



KEGULATION OF HEAT! 



241 



body possesses of resisting the effects of a high tempera- 
ture, in virtue of evaporation from the skin. 

Sir Charles Blagden and others supported a temperature 
varying between 198° and 211° F. in dry air for several 
minutes; and in a subsequent experiment he remained 
eight minutes in a temperature of 260°. But such heats 
are not tolerable when the air is moist as weU as hot, so 
as to prevent evaporation from the body. Mr. C. James 
states, that in the vapour baths of Nero he was almost 
suffocated in a temperature of 1 12°, while in the caves of 
Testaccio, in which the air is dry, he was but little incom- 
moded by a temperature of 176°. In the former, evapo- 
ration from the skin was impossible ; in the latter, it was, 
probably, abundant, and the layer of vapour which would 
rise from all the surface of the body would, by its very 
slowly conducting power, defend it for a time from the full 
action of the external heat. 

(The glandular apparatus, by which secretion of fluid 
from the skin is effected, will be considered in the Section 
on the Skin.) 

The ways by which the skin may be rendered more 
efficient as a cooling- apparatus by exposure, by baths, and 
by other means, which man instinctively adopts for lower- 
ing his temperature when necessary, are too well known to 
need more than to be mentioned. 

As a means for lowering the temperature, the lungs and 
air-passages are very inferior to the skin ; although, by 
giving heat to the air we breathe, they stand next to the 
skin in importance. As a regulating power, the inferiority 
is still more marked. The air which is expelled from 
the lungs leaves the body at about the temperature of 
the blood, and is always saturated with moisture. No 
inverse proportion, therefore, exists between the loss of 
heat by radiation and conduction on the one hand, and 
by evaporation on the other. The colder the air, for 
example, the greater will be the loss in all ways. Neither 



242 



ANIMAL HEAT. 



is the quantity of blood which is exposed to the cooling 
influence of the air diminished or increased, so far as is 
known, in accordance with any need in relation to tempe- 
rature. It is true that by varying the number and depth 
of the respirations, the quantity of heat given off by the 
lungs may be made, to some extent, to vary also. But the 
respiratory passages, while they must be considered important 
means by which heat is lost, are altogether subordinate in 
the power of regulating the temperature, to the skin. 

It may seem to have been assumed, in the foregoing 
pages, that the only regulating apparatus for temperature 
required by the human body is one that shall, more or less, 
produce a cooling effect ; and as if the amount of heat pro- 
duced were always, therefore, in excess of that which is 
required. Such an assumption would be incorrect. We 
have the power of regulating the production of heat, as 
well as its loss. 

In food we have a means for elevating our temperature. 
It is the fuel, indeed, on which animal heat ultimately 
depends altogether. Thus, when more heat is wanted, we 
instinctively take more food, and take such kinds of it as 
are good for combustion ; while everyday experience shows 
the different power of resisting cold possessed by the well- 
fed and by the starved. 

In northern regions, again, and in the colder seasons of 
more southern climes, the quantity of food consumed is 
(speaking very generally) greater than that consumed by 
the same men or animals in opposite conditions of climate 
and seasons. And the food which appears naturally 
adapted to the inhabitants of the coldest climates, such as 
the several fatty and oily substances, abounds in carbon 
and hydrogen, and is fitted to combine with the large 
quantities of oxygen which, breathing cold dense air, they 
absorb from their lungs. 

In exercise, again, we have an important means of 
raising the temperature of our bodies (p. 233). 



INFLIJEXCE OF NERVOUS SYSTEM. 



243 



The influence of external coverings for the body must not 
be unnoticed. In warm-blooded animals, they are always 
adapted, among other purposes, to the maintenance of 
uniform temperature ; and man adapts for himself such as 
are, for the same purpose, fitted to the various climates to 
which he is exposed. By their means, and by his command 
over food and fire, he maintains his temperature on all 
accessible parts of the surface of the earth. 

The influence of the nervous system in modifying the pro- 
duction of heat has been already referred to. The experi- 
ments and observations which best illustrate it are those 
showing, first, that when the supply of nervous influence 
to a part is cut ofi", the temperature of that part falls below 
its ordinary degree; and, secondly, that when death is 
caused by severe injury to, or removal of, the nervous 
centres, the temperature of the body rapidly falls, even 
though artificial respiration be performed, the circulation 
maintained, and to all appearance the ordinary chemical 
changes of the body be completely effected. It has been 
repeatedly noticed, that after division of the nerves of a 
limb, its temperature falls ; and this diminution of heat 
has been remarked still more plainly in limbs deprived of 
nervous influence by paralysis. For example, Mr. Earle 
found the temperature of the hand of a paralysed arm to 
be 70°, while the hand of the sound side had a tempera- 
ture of 92° F. On electrifying the paralysed limb, the 
temperature rose to 77°. In another case, the temperature 
of the paralysed finger was 56° F., while that of the un- 
affected hand was 62°. 

With equal certainty, though less definitely, the influence 
of the nervous system on the production of heat, is shown 
in the rapid and momentary increase of temperature, 
sometimes general, at other times quite local, which is 
observed in states of nervous excitement ; in the general 
increase of warmth of the body, sometimes amounting to 
perspiration, which is excited by passions of the mind ; in 

11 2 



244 ANIMAL HEAT. 

the sudden rush of heat to the face, which is not a mere 
sensation ; and in the equally rapid diminution of tem- 
perature in the depressing passions. But none of these 
instances suf&ces to prove that heat is generated by mere 
nervous action, independent of any chemical change ; all 
are explicable, on the supposition that the nervous system 
alters, by its power of controlling the calibre of the blood- 
vessels (p. 141), the quantity of blood supplied to a part; 
while any influence which the nervous system may have in 
the production of heat apart from this influence on the 
blood-vessels, is an indirect one, and is derived from 
its power of causing nutritive change in the tissues, which 
may, by involving the necessity of chemical action, involve 
the production of heat. The existence of nerves, which 
regulate animal heat otherwise than by their influence 
in trophic (nutritive) or vaso-motor changes, although by 
many considered probable, is not yet proven. 

In connection with the regulation of animal tempera- 
ture, and its maintenance in health at the normal height, 
it is interesting to note the result of circumstances too 
powerful, either in raising or lowering the heat of the body, 
to be controlled by the proper regulating apparatus. 
Walther foiind that rabbits and dogs, when tied to a board 
and exposed to a hot sun, reached a temperature of 
114*8° F., and then died. Cases of sunstroke furnish us 
with similar examples in the case of man ; for it would 
seem that here death ensues chiefly or solely from elevation 
of the temperature. In a case related by Dr. Gee, the 
temperature in the axilla was 109*5° F. : and in many 
febrile diseases the immediate cause of death appears to be 
the elevation of the temperature to a point inconsistent 
with the continuance of life. 

The effect of mere loss of bodily temperature in man is 
less well known than the effect of heat. 

From experiments by Walther, it appears that rabbits 
can be cooled down to 48° F. before they die, if artificial 



FOOD. 



245 



respiration be kept up. Cooled down to 64° F., they can- 
not recover unless external warmtli be applied together 
with the employment of artificial respiration. Rabbits 
not cooled below 77° F. recover by external warmth 
alone. 



CHAPTER IX. 

DIGESTION. 



Digestion is the process by which those parts of our 
food which may be employed in the formation and repair 
of the tissues, or in the production of heat, are made fit to 
be absorbed and added to the blood. 

Food. 

Food may be considered in its relation to these two pur- 
poses — the nutrition of the tissues, and the production of 
heat. But, under the first of these heads will be included 
many other allied functions, as, for example, secretion and 
generation : and under the second, not the production of 
heat only as such, but of all the other forces correlated 
with it, which are manifested by the living body. 

The following is a convenient tabular classification of 
the usual and more necessary kinds of food : — 

Nitrogenous : — 

Proteids, as Albumen, Casein, Syntonin, Gluten, and their allies, 
and Gelatin ; (containing Carbon, Hydrogen, Oxygen, and Nitrogen ; 
some of tliem, also Sulphur and Phosphorus). 

NoN-NlTROGENOTTS : 

(i). Amyloids — Starch, Sugar, and their allies (containing Carbon, 
Hydrogen and Oxygen). 

(2). Oils and Fats (containing Carbon, Hydrogen, and Oxygen ; the 
oxygen in much smaller proportion than in starch or sugar). 

(3). Mineral or Saline Matters ; as Chloride of Sodium, Phosphate of 
Lime, etc. 

(4). Water. 



246 DIGESTION. 

Animals cannot subsist on any but organic substances, 
and these must contain the several elements and com- 
pounds which are naturally combined with them : in other 
words, not even organic compounds are nutritive unless 
they are supplied in their natural state. Pure fibrin, pure 
gelatin, and other principles purified from the substances 
naturally mingled with them, are incapable of supporting 
life for more than a brief time. 

Moreover, health cannot be maintained by any number 
of substances derived exclusively from one only of the two 
chief groups of alimentary j)rinciples mentioned above. A 
mixture of nitrogenous and non-nitrogenous organic sub- 
stances, together with the inorganic principles which are 
severally contained in them, is essential to the well-being 
and, generally, even to the existence of an animal. The 
truth of this is demonstrated by experiments performed for 
the purpose, and is illustrated by the composition of the 
food prepared by nature as the exclusive source of nou- 
rishment to the young of Mammalia, namely, milk. 

Composition of Milk. 

Human. Cows. 

Water . . . . 890 . . . .858 
Solids . . . . no . . . . 142 

1, 000 1,000 

Casein . . . • 35 • . • .68 

Butter . . . . 25 . . . . 38 

Sugar (with extractives) 48 . . . .30 

Salts .... 2 .... 6 

no 142 

In milk, as will be seen from the preceding table, the 
albuminous group of aliments is represented by the casein, 
the oleaginous by the butter, the aqueous by the water, 
the saccharine by the sugar of milk. Among the salts of 
milk are likewise phosphate of lime, alkaline, and other 
salts, and a trace of iron ; so that it may be briefly said 



COMPOSITION OF EGGS. 247 

to include all the substances wliicli the tissues of the 
growing animal need for their nutrition, and which are 
required for the production of animal heat. 

The yelk and albumen of eggs are in the same relation 
as food for the embryoes of oviparous animals, that milk is 
to the young of Mammalia, and afford another example of 
mixed food being provided as the most perfect nutrition. 

CoMPOsiTiox OF Fowls' Eggs. 





White. 




Yelk. 


Water 


. 8o-o 


. 


5373 


Albumen 


• . 15-5 


. 


. 17-47 


Mucus 


. 4-5 


Yellow Oil 


2875 


Salts . 


. . 4'o 


• 


6-0 
_i- 1 



Experiments illustrating the same principle have been 
performed by Magendie and others. Dogs were fed ex- 
clusively on sugar and distilled water. During the first 
seven or eight days they were brisk and active, and took 
their food and drink as usual ; but in the course of the 
second week, they began to get thin, although their appe- 
tite continued good, and they took daily between six and 
eight ounces of sugar. The emaciation increased during 
the third week, and they became feeble, and lost their 
activity and appetite. At the same time an ulcer formed 
on each cornea, followed by an escape of the humours of 
the eye : this took place in repeated experiments. The 
animals still continued to eat three or four ounces of sugar 
daily ; but became at length so feeble as to be incapable of 
motion, and died on a day varying from the thirty-first to 
the thirty-fourth. On dissection, their bodies presented all 
the appearances produced by death from starvation; in- 
deed, dogs wiU live almost the same length of time without 
any food at all. 

When dogs were fed exclusively on gum, results almost 
similar to the above ensued. When they were kept on 
olive-oil and water, all the phenomena produced were the 
same, except that no ulceration of the cornea took place : 



248 DIGESTIOX. 

tlie effects were also the same with butter. Tiedemann 
and Gmelin obtained very similar results. They fed 
different geese, one with sugar and water, another with 
gum and water, and a third with starch and water. All 
gradually lost weight. The one fed with gum died on the 
sixteenth day ; that fed with sugar, on the twenty-second ; 
the third, which was fed with starch, on the twenty-fourth ; 
and another on the twenty-seventh day; having lost, 
during these periods, from one-sixth to one-half of their 
weight. The experiments of Chossat and Letellier prove 
the same ; and in men, the same is shown by the various 
diseases to which they who consume but little nitrogenous 
food are liable, and especially, as Dr. Budd has shown, 
by the affection of the cornea which is observed in Hindus 
feeding almost exclusively on rice. But it is not only the 
non-nitrogenous substances, which, taken alone, are in- 
sufficient for the maintenance of health. The experiments 
of the Academies of France and Amsterdam were equally 
conclusive that gelatin alone soon ceases to be nu- 
tritive. 

Mr. Savory's obseivations on food confirm and extend 
the results obtained by Magendie, Chossat, and others. 
They show that animals fed exclusively on non-nitrogenous 
diet speedily emaciate and die, as if from starvation ; that 
a much larger amount of urine is voided by those fed with 
nitrogenous than by those with non-nitrogenous food ; and 
that animal heat is maintained as well by the former as 
by the latter — a fact which proves that nitrogenous elements 
of food, as well as non-nitrogenous may be regarded as 
calorifacient. ,The non-nitrogenous principles, however, 
he believes to be calorifacient essentially, not being first 
converted into tissue ; but of the nitrogenous, he believes 
that only a part is thus directly calorifacient, the rest 
being employed in the formation of tissue. Contrary to 
the views of Liebig and Lehmann, Savory has shown that, 
while animals speedily die when confined to non-nitro- 



EXPERIMENTS WITH DIFFERENT FOODS. 



249 



genoTis diet, they may live long when fed exclusively with 
nitrogenous food. 

Man is supported as well by food constituted wholly of 
animal substances, as by that which is formed entirely of 
vegetable matters, on the condition, of course, that it 
contain a mixture of the various nitrogenous and non 
nitrogenous substances just shown to be essential for 
healthy nutrition. In the case of carnivorous animals, the 
food upon which they exist, consisting as it does of the 
flesh and blood of other animals, not only contains all the 
elements of which their own blood and tissues are com- 
posed, but contains them combined, probably in the same 
forms. Therefore little more may seem requisite, in the 
preparation of this kind of food for the nutrition of the 
body, than that it should be dissolved and conveyed into 
the blood in a condition capable of being re-organized. 
But in the case of the herbivorous animals, which feed ex- 
clusively upon vegetable substances, it might seem as if. 
there would be greater difficulty in procuring food capable 
of assimilation into their blood and tissues. But the chief 
ordinary articles of vegetable food contain, substances 
identical in composition, with the albumen, fibrin, and 
casein, which constitute the principal nutritive materials in 
animal food. Albumen is abundant in the juices and 
seeds of nearly all vegetables; the gluten which exists, 
especially in corn and other seeds of grasses as well as in 
their juices, is identical in composition with fibrin, and is 
often named vegetable fibrin ; and the substance named 
legumen, which is obtained especially from peas, beans, 
and other seeds of leguminous plants, and from the potato, 
is identical with the casein of milli. All these vegetable 
substances are, equally with the corresponding animal 
principles, and in the same manner, capable of conversion 
into blood and tissue ; and as the blood and tissues in both 
classes of animals are alike, so also the nitrogenous food of 
both may be regarded as, in essential respects, similar. 



250 DIGESTION. 

It is in the relative quantities of the nitrogenous and 
non-nitrogenous compounds in these different foods that 
the difference lies, rather than in the presence of substances 
in one of them which do not exist in the other. The only 
non- nitrogenous compounds in ordinary animal food are 
the fat, the saline matters, and water, and, in some in- 
stances, the vegetable matters which may chance to be in 
the digestive canals of such animals as are eaten whole. 
The amount of these, however, is altogether much less 
than that of the non-nitrogenous substances represented by 
the starch, sugar, gum, oil, etc., in the vegetable food of 
herbivorous animals. 

The effects of total deprivation of food have been made 
the subject of experiments on the lower animals, and have 
been but too frequently illustrated in man. 

(l). One of the most notable effects of starvation, as 
might be expected, is loss of weight; the loss being greatest 
at first, as a rule, but afterwards not varying very much, 
day by day, until death ensues. Chossat found that the 
idtimate proportional loss was, in different animals experi- 
mented on, almost exactly the same; death occurring 
when the body had lost two-fifths (forty per cent.) of its 
original weight. 

Different parts of the body lose weight in very different 
proportions. The following results are taken, in round 
numbers, from the table given by M. Chossat : — 



Tat loses 93 per cent. 

Blood 75 M 

Spleen 71 ,, 

Pancreas 64 ,, 

Liver 52 ,, 

Heart 44 >. 

Intestines 42 ,, 

Muscles of locomotion , . , 42 , , 

Stomach loses . • • -39 >> 



STARVATION. 



251 



Pharynx, ((Esophagus) 

Skin . . . . 

Kidneys . 

Respiratory apparatus 

Bones 

Eyes .... 

Nervous system 



34 per cent. 
33 
31 
22 
16 
10 
2 



(nearly). 



(2) . The effect of starvation on the temperature of the 
various animals experimented on by Chossat was very 
marked. For some time the variation in the daily tempe- 
rature was more marked than its absolute and continuous 
dimunition, the daily fluctuation amounting to 5° or 6° F., 
instead of 1° or 2° F., as in health. But a short time 
before death, the temperature fell very rapidly, and death 
ensued when the loss had amounted to about 30° F. It has 
been often said, and with truth, although the statement 
requires some qualification, that death by starvation is 
really death by cold ; for not only has it been found that 
differences of time with regard to the period of the fatal 
result are attended by the same ultimate loss of heat, but 
the effect of the application of external warmth to animals 
cold and dying from starvation, is more effectual in reviving 
them than the administration of food. In other words, an 
animal exhausted by deprivation of nourishment is unable 
so to digest food as to use it as fuel, and therefore is de- 
pendent for heat on its supply from without. Similar 
facts are often observed in the treatment of exhaustive 
diseases in man. 

(3). The symptoms produced by starvation in the human 
subject are hunger, accompanied, or it may be replaced, 
by pain, referred to the region of the stomach ; insatiable 
thirst ; sleeplessness ; general weakness and emaciation. 
The exhalations both from the lungs and skin are foetid, 
indicating the tendency to decomposition which belongs 
to badly-nourished tissues; and death occurs, sometimes 
after the additional exhaustion caused by diarrhoea, often 



252 DIGESTIOX. 

with, symptoms of nervous disorder, delirium, or con- 
vulsions. 

(4). In tlie human subject death commonly occurs 
within six to ten days after total deprivation of food. But 
this period may be considerably prolonged by taking a 
very small quantity of food, or even water only. The 
cases so frequently related of survival after many days^ or 
even some weeks, of abstinence, have been due either to 
the last-mentioned circumstances, or to others less effectual, 
which prevented the loss of heat and moisture. Cases in 
which life has continued after total abstinence from food 
and drink for many weeks, or months, exist only in the 
imagination of the vulgar. 

(5). The appearances presented after death from starva- 
tion are those of general wasting and bloodlessness, the 
latter condition being least noticeable in the brain. The 
stomach and intestines are empty and contracted, and the 
walls of the latter usually appear remarkably thinned and 
almost transparent. The usual secretions are scanty or 
absent, with the exception of the bile, which, somewhat 
concentrated, usually fills the gall-bladder. All parts of 
the body readily decompose. 

It has just been remarked that man can live upon 
animal matters alone, or upon vegetables. The structure 
of his teeth, however, as well as experience, seems 
to declare that he is best fitted for a mixed diet ; and 
the same inference may be readily gathered from other 
facts and considerations. Thus, the food a man takes 
into his body daily, represents or ought to represent the 
quantity and kind of matter necessary for replacing that 
which is daily cast out by the way of lungs, skin, kidneys, 
and other organs. To find out, therefore, the quantity 
and kind of food necessary for a healthy man, it wiU, 
evidently, be the best plan to consider in the first place 
what he loses by excretion. 



DAILY LOSS OF CARBOX AND NITROGEJs\ 253 

For the sake of example, we may now take only two 
elements, carbon and nitrogen, and, if we discover what 
amount of these is respectively discharged in a given time 
from the body, we shall be in a position to judge what 
kind of food will most readily and economically replace 
their loss. 

The quantity of carbon daily lost from the body amounts 
to about 4,500 grains, and of nitrogen 300 grains; and ^d/ltS^ 
if a man could be fed by these elements, as such, the 
problem would be a very simple one; a corresponding 
weight of charcoal, and, allowing for the oxygen in it, 
of atmospheric air, would be all that is necessary. But, 
as before remarked, an animal can live only upon these 
elements when they are arranged in a particular man- 
ner with others, in the form of an organic compound, as 
albumen, starch, and the like; and the relative propor- 
tion of carbon to nitrogen in either of these compounds 
alone, is, by no means, the proportion required in the 
diet of man. The amount, 4,500 grains of carbon, repre- 
sents about fifteen times the quantity of nitrogen required 
in the same period; and, in albumen, the proportion of 
carbon to nitrogen is only as 3-5 to i. If, therefore, a man 
took into his body, as food, sufficient albumen to supply 
him with the needful amount of carbon, he would receive 
more than four times as much nitrogen as he wanted ; 
and if he took only sufficient to supply him with nitrogen, 
he would be starved for want of carbon. It is plain, 
therefore, that he should take with the albuminous part 
of his food, which contains so large a relative amount 
of nitrogen in proportion to the carbon he needs, sub- 
stances in which the nitrogen exists in much smaller 
quantities. 

Food of this kind is provided in such compounds as 
starch and fat. The latter indeed as it exists for the most 
part in considerable amount mingled with the flesh of 
animals, removes to a great extent, in a diet of animal ' 



254 DIGESTION. 

food, the difficulty which, would otherwise arise from a 
deficiency of carbon — fat containing a large relative pro- 
portion of this element, and no nitrogen. 

To take another example ; the proportion of carbon to 
nitrogen in bread is about 30 to I. If a man's diet were 
confined to bread, he would eat, therefore, in order to 
obtain the requisite quantity of nitrogen, twice as much 
carbon as is necessary; and it is evident, that, in this 
instance, a certain quantity of a substance with a large 
relative amount of nitrogen is the kind of food necessary 
for redressing the balance. 

To place the preceding facts in a tabular form, and 
taking meat as an example instead of pure albumen : — 
meat contains about 10 per cent, of carbon, and rather 
more than 3 per cent, of nitrogen. Supposing a man to 
take meat for the supply of the needful carbon, he would 
require 45,000 grains, or nearly 6 jibs., containing : — 

Carbon 4, 5<X) grains 

Nitrogen 1,350 „ 

Excess of Nitrogen above the amount required 1,500 „ 

Bread contains about 30 per cent, of carbon and i per 
cent, of nitrogen. 

If bread alone, therefore, were taken as food, a man 
would require, in order to obtain the requisite nitrogen, 
30,000 grains, containing — 

Carbon 9,000 grains 

Nitrogen 300 ,, 

Excess of Carbon above tlio amoimt required . 4,500 ,, 

But a combination of bread and meat would supply 
much more economically what was necessary. Thus — 

Carbon. Nitrogen. 
15,000 grains of bread (or rather more than 

2 lbs.) contain 4,500 grs. 150 grs. 

5,000 gi-ains of meat (or about | lb.) contain 500 ,, 150 ,, 

5,000 ,, 300 „ 



NECESSITY FOR CHANGES OF DIET. 255 

So that f lb. of meat, and less than 2 lbs. of bread, 
would supply all the needful carbon and nitrogen with but 
little waste. 

From these facts it wiU be plain that a mixed diet is the 
best and most economical food for man ; and the residt of 
experience entirely coincides with what might have been 
anticipated on theoretical grounds only. 

It must not be forgotten, however, that the value of 
certain foods may depend quite as much on their digesti- 
bility, as on the relative quantities of the necessary 
elements which they contain. 

In actual practice, moreover, the quantity and kind of 
food to be taken with most economy and advantage cannot 
be settled for each individual, only by considerations of the 
exact quantities of certain elements that are required. 
Much will] of necessity depend on the habits and digestive 
powers of the individual, on the state of his excretory 
organs, and on many other circumstances. Food which to 
one person is appropriate enough, may be quite unfit for 
another ; and the changes of diet so instinctively prac- 
tised by all to whom they are possible, have much more 
reliable grounds of justification than any which could be 
framed on theoretical considerations only. 

In many of the experiments on the digestibility of 
various articles of food, disgust at the sameness of the 
diet may have had as much to do with inability to consume 
and digest it, as the want of nutritious properties in the 
substances which were experimented on. And that disease 
may occur from the want of particular food, is well shown 
by the occurrence of scurvy when fresh vegetables are 
deficient, and its rapid cure when they are again eaten : 
and the disease which is here so remarkably evident in its 
symptoms, causes, and cure, is matched by numberless 
other ailments, the causes of which, however, although 
analogous, are less exactly known, and therefore less 
easily combated. 



256 DIGESTION. 

With regard to the quantity, too, as well as the kind of 
food necessary, there will be much diversity in different 
individuals. Dr. Dalton believed, from some experiments 
which he performed, that the quantity of food necessary 
for a healthy man, taking free exercise in the open air, is 
as follows: — 



Meat . 


. 


. 16 ounces, or i*oo lb. avoii-d. 


Bread 


. 


. 19 ,, „ I-I9 „ „ 


Butter or Fat. 


. 


. 3h „ „ 0-22 „ „ 


Water 


. 


52 fluid ozs. 3*38 „ ,, 



\ 

The quantity of meat, however, here given, is probably 
more in proportion to the other articles of diet enumerated 
than is needful for the majority of individuals under the 
circumstances stated. 

PASSAGE OF FOOD THROUGH THE ALIMENTARY CANAL. 

The course of the food through the alimentary canal of 
man will be readily seen from the accompanying diagram 
(fig. 66). The food taken into the mouth passes thence 
through the oesophagus into the stomach, and from this 
into the small and large intestine successively; gradually 
losing, by absorption, the greater portion of its nutritive 
constituents. The residue, together with such matters as 
may have been added to it in its passage, is discharged 
from the rectum through the anus. 

We shall now consider, in detail, the process of diges- 
tion, as it takes place in each stage of this journey of the 
food through the alimentary canal. 

The Salivary Glands and the Saliva.. 

The first of a series of changes to which the food is sub- 
jected in the digestive canal, takes place in the cavity of 
the mouth ; the solid articles of food are here submitted to 
the action of the teeth (p. 59), whereby they are divided 



SALIVARY GLANDS AND SALIVA. 



257 



and crushed, and by being at tbe same time mixed with 
the fluids of the mouth, are reduced to a soft pulp, capable 

Fig. 66.* 




of being easily swallowed. The fluids with which the food 
is mixed in the mouth consist of the secretion of the 



* Fig. 66. Diagram of the alimentary canal. The small intestine 
of man is from about 3 to 4 times as long as the large intestine. 



258 



DIGESTION. 



salivary glands, and the mucus secreted by tlie lining 
membrane of the whole buccal cavity. 

The glands concerned in the production of saliva, are 
very extensive, and, in man and Mammalia generally, are 
presented in the form of four pairs of large glands, the 
parotid, submaxillary, sublingual, and numerous smaller 
bodies, of similar structure and with separate ducts, which 
are scattered thickly beneath the mucous membrane of the 
lips, cheeks, soft palate, and root of the tongue. The 
structure of all these glands is essentially the same. Each 
is composed of several parts, called lobes, which are joined 
together by areolar tissue ; and each of these lobes, again, 
is made up of a number of smaller parts, called lobules, 
bound together as before by areolar tissue. Each of these 
small divisions, called lobules, is a miniature representation 
of the whole gland. It contains a small branch of the 
duct, which, subdividing, ends in small vesicular pouches, 
called acini, a group of which may be considered the 




dilated end of one of the smaller ducts (fig. 67) . Each of 
the acini is about -jl^ of an inch in diameter, and is formed 
of a fine structureless membrane, lined on the inner surface 
and often filled by spheroidal or glandular epithelium; 



Fig. 67. Diagram of a racemose or saccular compound gland ; w, 
entire gland, showing branched duct and lobidar structure ; n, a lobule 
detached, with 0, branch of duct proceeding from it (after Sharpey). 



SALIVA. 259 

while on- the outside there is a plexus of capillary blood- 
vessels. The accompanying diagram is intended to show 
the typical structure of such glands as the salivary (fig. ^j^. 

Saliva, as it commonly flows from the mouth, is mixed 
with the secretion of the mucous membrane, and often 
with air bubbles, which, being retained by its viscidity, 
make it frothy. 

When obtained from the parotid ducts, and free from 
mucus, saliva is a transparent watery fluid, the specific 
gravity of which varies from 1*004 ^^ I "008, and in which, 
when examined with the microscope, are found floating a 
number of minute particles, derived from the secreting 
ducts and vesicles of the glands. In the impure or mixed 
saliva are found, besides these particles, numerous epithelial 
scales separated from the surface of the mucous membrane 
of the mouth and tongue, and mucus-corpuscles, discharged 
for the most part from the tonsils, which, when the saliva 
is collected in a deep vessel, and left at rest, subside in the 
form of a white opaque matter, leaving the supernatant 
salivary fluid transparent and colourless, or with a pale 
bluish-grey t'nt. In reaction^ the saliva, when flrst secreted, 
appears to be always alkaline ; and . that from the parotid 
gland is said to be more strongly alkaline than that from 
the other salivary glands. This alkaline condition is most 
evident when digestion is going on, and according to 
Dr. Wright, the degree of alkalinity of the saliva bears a 
direct proportion to the acidity of the gastric fluid secreted 
at the same time. During fasting, the saliva, although 
secreted alkaline, shortly becomes neutral ; and it does so 
especially when secreted slowly and allowed to mix with 
the acid mucus of the mouth, by which its alkaline reaction 
is neutralized. 

The following analysis of the saliva is by Frerichs : — 



s 2 



26o 



DIGESTION. 



Composition of Saliva 



Water 994 'lo 


Solids 


5-90- 


Ptyalin 


I -41 


Fat 


0-07 


Epithelium and Mucus . 


2-is 


Salts :— 




Sulpho-Cyanide of Potassium . ^ 




Phosphate of Soda 




„ „ Lime . . . 




„ „ Magnesia . 


)2-29 


Chloride of Sodium . . . 




,, ,, Potassium . . ^ 





5 "90 

The rate at which saliva is secreted is subject to consider- 
able variation. When the tongue and muscles concerned 
in mastication are at rest, and the nerves of the mouth, 
are subject to no unusual stimulus, the quantity secreted is 
not more than sufficient, with the mucus, to keep the mouth 
moist. But the flow is mucb accelerated when the move- 
ments of mastication take place, and especially wben they 
are combined with the presence of food in the mouth. It 
may be excited also, even when the mouth is at rest, by 
the mental impressions produced by the sight or thought 
of food ; also by the introduction of food into the stomach. 
The influence of the latter circumstance was well shown in 
a case mentioned by Dr. Gairdner, of a man whose pharynx 
had been divided: the injection of a meal of broth into 
the stomach was followed by the secretion of from six to 
eight ounces of saliva. 

Under these varying circumstances, the quantity of saliva 
secreted in twenty-four hours varies also ; its average 
amount is probably from two to three pints in twenty-four 
hours. In a man who had a fistulous opening of the 
parotid duct, Mitscherlich found that the quantity of saliva 
discharged from it during twenty-four hours, was from two 



USES OF SALIVA. 26 1 

to three ounces ; and the saliva collected from the mouth 
during the same period, and derived from the other sali- 
vary glands, amounted to six times more than that from 
the one parotid. 

The purposes served hy saliva are of several kinds. In the 
first place, acting mechanically in conjunction with mucus, 
it keeps the mouth in a due condition of moisture, facilitat- 
ing the movements of the tongue in speaking, and the mas- 
tication of food. (2.) It serves also in dissolving sapid 
substances, and rendering them capable of exciting the 
nerves of taste. But the principal mechanical purpose of 
the saliva is, (3) that by mixing with the food during mas- 
tication, it makes it a soft pulpy mass, such as may be 
easily swallowed. To this purpose the saliva is adapted 
both by quantity and quality. For, speaking generally, 
the quantity secreted during feeding is in direct proportion 
to the dryness and hardness of the food : as M. Lassaigne 
has shown, by a table of the quantity produced in the mas- 
tication of a hundred parts of each of several kinds of food, 
thirty parts suffice for a hundred parts of crumb of bread, 
but not less than 120 for the crusts ; 42*5 parts of saliva 
are produced for the hundred of roast meat; 3*7 for as 
much of apples ; and so on, according to the general rule 
above stated. The quality of saliva is equally adapted to 
this end. It is easy to see how much more readily it mixes 
with most kinds of food than water alone does ; and M. 
Bernard has shown that the saliva from the parotid, labial, 
and other small glands, being more aqueous than the rest, 
is that which chiefly braided and mixed with the food in 
mastication ; while the more viscid mucoid secretion of the 
submaxillary, palatine, and tonsillitic glands is spread over 
the surface of the softened mass, to enable it to slide more 
easily through the fauces and oesophagus. This view ob- 
tains confirmation from the interesting fact pointed out by 
Professor Owen, that in the great ant-eater, whose enor- 
mously elongated tongue is kept moist by a large quantity 



262 DIGESTIOK 

of viscid saliva, the submaxillary glands are remarkably 
developed, while the parotids are not of unusual size. 

Beyond these, its mechanical purposes, saliva performs 
(4) a chemical part in the digestion of the food. When 
saliva, or a portion of a salivary gland, or even a portion 
of dried ptyalin, is added to starch paste, the starch is very 
rapidly transformed into dextrin and grape-sugar; and 
when common raw starch is masticated and mingled with 
saliva, and kept with it at a temperature of 90° or 1 00°, 
the starch-grains are cracked or eroded, and their contents 
are transformed in the same manner as the starch-paste. 
Changes similar to these are effected on the starch of fari- 
naceous food (especially after cooking) in the stomach ; and 
it is reasonable to refer them to the action of the saliva, be- 
cause the acid of the gastric fluid tends to retard or prevent, 
rather than favour the transformation of the starch. It 
may therefore be held, that one purpose served by the 
saliva in the digestive process is that of assisting in the 
transformation of the starch, which enters so largely 
into the composition of most articles of vegetable food, 
and which (being naturally insoluble) is converted into 
soluble dextrin and grape-sugar, and made fit for ab- 
sorption. 

Besides saliva, many azotized substances, especially if in 
a state of incipient decomposition, may excite the trans- 
formation of starch, such as pieces of the mucous mem- 
brane of the mouth, bladder, rectum, and other parts, 
various animal and vegetable tissues, and even morbid 
products ; but the gastric fluid will not produce the same 
effect. The transformation in question is effected much 
more rapidly by saliva, however, than by any of the other 
fluids or substances experimented with, except the pan- 
creatic secretion, which, as will be presently shown, is very 
analogous to saliva. The actual process by which these 
changes are effected is still obscure. Probably the azotized 
substance, ptyalin, acts as a kind of ferment, like diastase 



DEGLUTITION. 26^ 

in the process of malting, and excites molecular changes in 
the starch which result in its transformation, first into 
dextrin and then into sugar. 

The majority of observers agree that the transformation 
of starch into sugar ceases on the entrance of the food into 
the stomach, or on the addition of gastric fluid to it in 
a test-tube ; while others maintain that it still goes on. 
Probably all are right : for, although gastric fluid added 
to saliva appears to arrest the action of the latter on 
starch, yet portions of saliva mingled with food in mas- 
tication may, for some time after their entrance into the 
stomach, remain unneutralized by the gastric secretion, 
and continue their influence upon the starchy principles 
in contact with them. 

Starch appears to be the only principle of food upon 
which saliva acts chemically : it has no apparent influence 
on any of the other ternary principles, such as sugar, gum, 
cellulose, or (according to Bernard) on fat, and seems to be 
equally destitute of power over albuminous and gelatinous 
substances, so that we have as yet no information respect- 
ing any purpose it can serve in the digestion of Carnivora, 
beyond that of softening or macerating the food ; though, 
since such animals masticate their food very little, usually 
"bolting" it, the saliva has probably but little use even in 
this respect, in the process of digestion. 

Passage of Food into the Stomach. 

When properly masticated, the food is transmitted in 
successive portions to the stomach by the act of der/lutition 
or swallowing. This act, for the purpose of description, 
may be divided into three parts. In the first, particles of 
food collected to a morsel glide bet\Yeen the surface of the 
tongue and the palatine arch, till they have passed the , 
anterior arch of the fauces ; in the second, the morsel is 
carried through the pharynx ; and in the third, it reaches 
the stomach through the oesophagus. These three acts 



264 DIGESTION. 

follow eacli otlier rapidl3\ The first is performed volun- 
tarily by the muscles of the tongue and cheeks. The second 
also is effected with the aid of muscles which are in part 
endued with voluntary motion, such as the muscles of the 
soft palate and pharynx ; but it is, nevertheless, an invo- 
luntary act, and takes place without our being able to 
prevent it, as soon as a morsel of food, drink, or saliva is 
carried backwards to a certain point of the tongue's sur- 
face. When we appear to swallow voluntarily, we only 
convey, through the first act of deglutition, a portion 
of food or saliva beyond the anterior arch of the palate ; 
then the substance acts as a stimulus, which, in accordance 
with the laws of reflex movements hereafter to be described, 
is carried by the sensitive nerves to the medulla oblongata, 
when it is reflected by the motor nerves, and an involuntary- 
adapted action of the muscles of the palate and pharynx 
ensues. The third act of deglutition takes place in the 
oesophagus, the muscular fibres of which are entirely beyond 
the influence of the will. 

The second act of deglutition is the most complicated, 
because the food must pass by the posterior orifice of the 
nose and the upper opening of the larynx without touching 
them. When it has been brought, by the first act, between 
the anterior arches of the palate, it is moved onwards by 
the tongue being carried backwards, and by the muscles of 
the anterior arches contracting on it and then behind it. 
The root of the tongue being retracted, and the larynx 
being raised with the pharynx and carried forwards under 
the tongue, the epiglottis is pressed over the upper opening 
of the larynx, and the morsel glides past it ; the closure of 
the glottis being additionally secured by the simultaneous 
contraction of its own muscles : so that, even when the 
epiglottis is destroyed, there is little danger of food or drink 
passing into the larynx so long as its muscles can act freely. 
At the same time the raising of the soft palate, so that its 
posterior edge touches the back x>art of the pharynx, and 



STRUCTUEE OF THE STOMACH. 265 

tlie approximation of the sides of the posterior palatine 
arch, which move quickly inwards like side curtains, close 
the passage into the upper part of the pharynx and the pos- 
terior nares, and form an inclined plane, along the under 
surface of which the morsel descends ; then the pharynx, 
raised up to receive it, in its turn contracts, and forces it 
onwards into the oesophagus. 

In the third act, in which the food passes through the 
oesophagus, every part of that tube as it receives the morsel 
and is dilated by it, is stimulated to contract: hence an 
undulatory contraction of the oesophagus, which is easily 
observable in horses while drinking, proceeds rapidly along 
the tube. It is only when the morsels swallowed are large, 
or taken too quickly in succession, that the progressive 
contraction of the oesophagus is slow, and attended with 
pain. Division of both pneumogastric nerves paralyzes the 
contractile power of the oesophagus, and food accordingly 
accumulates in the tube (Bernard). 

DIGESTION OF FOOD IN THE STOMACH. 

Structure of the Stomach. 

It appears to be an almost universal character of animals, 
that they have an internal cavity for the production of a 
chemical change in the aliment — a cavity for digestion; 
and when this cavity is compound, the part in which the 
food undergoes its principal and most important changes is 
the stomach. 

In man and those Mammalia which are provided with a 
single stomach, its walls consist of three distinct layers or^ 
coats, viz., an external peritoneal, an internal mucous, 
and an intermediate muscular coat, with blood-vessels, 
lymphatics, and nerves distributed in and between them. 

The muscular coat of the stomach consists of three sepa- 
rate layers or sets of fibres, which, according to their several 
directions, are named the longitudinal, circular, and oblique. 
The longitudinal set are the most superficial : they are con- 



266 DIGESTION. 

tinuous with the longitudinal fibres of the oesophagus, and 
spread out in a diverging manner over the great end and 
sides of the stomach. They extend as far as the pylorus, 
being especially distinct at the lesser or upper curvature of 
the stomach, along which they pass in several strong bands. 
The next set are the circular or transverse fibres, which more 
or less completely encircle all parts of the stomach ; they 
are most abundant at the middle and in the pyloric portion 
of the organ, and form the chief part of the thick project- 
ing ring of the pylorus. According to Pettigrew, these 
fibres are not simple circles, but form double or figure- 
of 8 loops, the fibres intersecting very obliquely. The next, 
and consequently deepest set of fibres, are the oblique, con- 
tinuous with the circular muscular fibres of the oesophagus, 
and, according to Pettigrew, with the same double -looped 
arrangement that prevails in the preceding layer: they 
are comparatively few in number, and are placed only at 
the cardiac orifice and portion of the stomach, over both 
surfaces of which they are spread, some passing obliquely 
from left to right, others from right to left, around the 
cardiac orifice, to which, by their interlacing, they form a 
kind of sphincter, continuous with that around the lower 
end of the oesophagus. The fibres of which the several 
muscular layers of the stomach, and of the intestinal canal 
generally, are composed, belong to the class of organic 
muscle, being composed of smooth or unstriped, elongated, 
spindle-shaped fibre-ceUs ; a fuller description of which 
will be given under the head of Muscular Tissue. 

The mucous membrane of the stomach, which rests upon 
a layer of loose cellular membrane, or submucous tissue, 
is smooth, level, soft, and velvety ; of a pale pink colour 
during life, and in the contracted state is thrown into 
numerous, chiefly longitudinal, folds or rugce, which dis- 
appear when the organ is distended. 

In its general structure the mucous membrane of the 
stomach resembles that of other parts (see Structure of 
Mucous Membrane). But there are certain peculiarities 



STRUCTURE OF THE STOMACH. 267 

shared with the mucous membrane of the small and large 
intestines, which, doubtless, are connected with the peculiar 
functions, especially those relating to absorption, which 
these parts of the alimentary canal perform. 

Entering largely into the construction of the mucous mem- 
brane, especially in the superficial part of the corium, is a 
quantity of a very delicate kind of connective tissue, called 
retiform tissue (fig. 72), or sometimes lymphoid or adenoid 
tissue, because it so closely resembles that which forms the 
stroma, or supporting framework of lymphatic glands (see 
Section on Lymphatic Glands) ; the resemblance being 
made much closer by the fact that the interspaces of this 
retiform tissue are filled with corpuscles not to be distin- 
guished from lymph-corpuscles. 

At the deepest part of the mucous membrane, is a 
layer of unstriped muscular fibres, called the muscularis 
mucosa), which must not be confounded with the layers of 
muscle constituting the proper muscular coat, and from 
which it is separated by the submucous tissue. The mus- 
cularis mucoscB is found in the oesophagus, as well as in 
the stomach and intestines. 

When examined with a lens, the internal or free surface 
of the stomach presents a peculiar honeycomb appearance, 
produced by shallow polygonal depressions or cells (fig. 6^), 
the diameter of which varies generally from -o-^th to 
•34-0 th of an inch ; but near the pylorus is as much as — J-o *h 
of an inch. They are separated by slightly elevated ridges^ 
which sometimes, especially in certain morbid states of the 
stomach, bear minute, narrow, vascular processes, which 
look like villi, and have given rise to the erroneous suppo- 
sition that the stomach has absorbing villi, like those of 
the small intestines. In the bottom of the cells minute 
openings are visible (fig. 6Z), which are the orifices of per- 
pendicularly arranged tubular glands (fig. 69) imbedded side 
by side in sets or bundles, in the substance of the mucous 
membrane, and composing nearly the whole structure. 



268 



DIGESTIOX. 



Fig. 68.^ 




The glands which, are found in the human stomach may 
be divided into two classes, the tulular and lenticular. 

Tubular Glands. The tubular 
glands may be described as a col- 
lection of cylinders with blind ex- 
tremities, about -^ th of an inch in 
length, and -jJ-tt in diameter, packed 
closely together, with their long axis 
at right angles to the surface of the 
mucous membrane on which they 
open, their blind ends resting on the submucous tissue. 
Fig. 69. t (See fig. 69.) They 

are all composed of 
basement mem- 
brane, and lined by 
epithelial cells, but 
they are not all 
of exactly similar 
shape; for while 
some are simple 
straight tubes, open 
at one end and 
closed at the other 
(fig. 69), others 
present at their 
deeper extremities 
Longitudinal avaricose,pouched, 

niuscr. libres. 

Peritoneum, or in somo cases, 
even a branched appearance (fig. 70, b and c). The 




* Fig. 68. Small portion of the surface of the mucous membrane of 
tlie stomacli (from Ecker) ^. — The specimen shows the shallow de- 
pressions, in each of which the smaller dark spots indicate the orifices 
of a variable number of the gastric tubular glands. 

t Fig. 69. Portion of human stomach (magnified 30 diameters, cut 
vertically, both in a direction ^jara??eZ to its long axis, and across it 
(altered from Brinton). 



GLANDS OF THE STOMACH. 



269 



epithelium lining them is not the same throughout. Iii 
the upper third or fourth of their length it is cylindricaly 




and continuous with that which covers the free mucous 
surface of the rest of the stomach. In their lower part, on 
the other hand, it is of the variety called glandular or sphe- 
roidal, the cells being oval or somewhat angular, and 
about -j^\ Q-th of an inch in diameter. The cells, however, 
do not completely fill up the cavity of the gland which they 
line, but leave a slight, central, thread-like space, the im- 
mediate lining of which is a layer of small angular cells,, 
continuous with the cylindrical epithelium in the upper 
portion of the tube. This description will become plain on 
reference to fig. 71, which represents on a larger scale a 
longitudinal section of one of the glands depicted in fig. 69- 



* Fig. 70. The gastric glands of the human stomach (magnified). 
a, deep part of a pyloric gastric gland (from Kolliker) ; the cylindrical 
epithelium is traceable to the csecal extremities, h and c, cardiac 
gastric glands (from Allen Thompson) ; h, vertical section of a small 
portion of the mucousmemhrane with the glands magnified 30 diameters ; 
c, deeper portion of one of the glands, magnified 65 diameters, showing 
a slight division of the tubes, and a sacculated appearance, produced 
by the large glandular cells within them ; d, cellular elements of the 
cardiac glands magnified 250 diameters. 



270 



DIGESTION. 



In the greater number of the glands which are branched 
at their deeper extremities, the spheroidal epithelium exists 
Fig. 71.* in the divisions, while the main duct 

and the upper part of the branches are 
lined by the cylindrical variety (fig. 
70, c). In the human stomach, ac- 
cording to Dr. Brinton, the simple un- 
divided tubes are the rule, and the 
branched the exception. 

The varieties in the epithelial cells 
lining the different parts of the tubes, 
correspond probably with differences 
in the fluid secreted by their agency — 
the cylinder-epithelium, like that on 
the free surface of the stomach being 
probably engaged in separating the 
thin alkaline mucus which is always 
present in greater or less quantity, 
while the larger glandular cells probably secrete the proper 
gastric juice. 

Near the pylorus there exist glands branched at their 
deep extremities, which are lined throughout by cylinder- 
epithelium (fig. 70, a), and probably serve only for the 
secretion of mucus. 

All the tubular glands, while they open by one end into 
the cavity of the stomach, rest by their blind extremities 
on a bed or matrix of areolar tissue (fig. 69), which is 
prolonged upwards between them, so as to invest and 
support them. 

Lenticular glands. — Besides the cylindrical glands, there 




* Fig. 71. Part of one of the gastric glands, highly magnified, to 
show the arrangement of the epithelium in its interior ; «, columnar 
cells lining the upper part of the tube ; h, small angular cells, into 
which these merge below to form a central or axial layer within ; c, the 
proper gastric or glandular cells (after Brinton). 



( 



THE GASTRIC FLUID. 27 1 

are also smaU closed sacs beneatli tlie surface of the 
mucous membrane, resem.bling exactly tbe solitary glands 
of the intestine, to be described hereafter. Their num- 
ber is very variable, and they are found chiefly along 
the lesser curvature of the stomach, and in the pyloric 
region, but they may be present in any part of the organ. 
According to Dr. Brinton they are rarely absent in children. 
Their function probably resembles that of the intestinal 
solitary glands, but nothing is certainly known regarding it. 

The blood-vessels of the stomach, which first break up 
in the submucous tissue, send branches upward between 
the closely packed glandular tubes, anastomosing around 
them by means of a fine capillary network with oblong 
meshes. Continuous with this deeper plexus, or prolonged 
upwards from it, so to speak, is a more superficial network 
of larger capillaries, which branch densely around the 
orifices of the tubes, and form the framework on which are 
moulded the small elevated ridges of mucous membrane 
bounding the minute, polygonal pits before referred to. 
From this superficial network the veins chiefly take their 
origin. Thence passing down between the tubes, with no 
very free connection with the deeper inter-tubular capillary 
plexus, they open finally into the venous network in the 
submucous tissue. 

The nerves of the stomach are derived from the pneumo- 
gastric and sympathetic. 

Secretion and Properties of the Gastric Fluid. 

AVhile the stomach contains no food, and is inactive, no 
gastric fluid is secreted ; and mucus, which is either 
neutral or slightly alkaline, covers its surface. But imme- 
diately on the introduction of food or other foreign sub- 
stance into the stomach, the mucous membrane, previously 
quite pale, becomes slightly turgid and reddened with the 
influx of a larger quantity of blood ; the gastric glands 
commence secreting actively, and an acid fluid is poured 



2/2 DIGESTION. 

out in minute drops, which gradually run together and flow 
down the walls of the stomach, or soak into the substances 
introduced. The quantity of this fluid secreted daily has 
been variously estimated ; but the average for a healthy 
adult has been assumed to range from ten to twenty pints 
in the twenty-four hours (Brinton). 

The first accurate analysis of the gastric jiuid was 
made by Dr. Prout : but it does not appear that it was 
collected in any large quantity, or pure and separate 
from food, until the time when Dr. Beaumont was 
enabled, by a fortunate circumstance, to obtain it from 
the stomach of a man named St. Martin, in whom there 
existed, as the result of a gunshot wound, an opening 
leading directly into the stomach, near the upper extremity' 
of the great curvature, and three inches from the cardiac 
orifice. The external opening was situate two inches 
below the left mamma, in a line drawn from that part 
to the spine of the left ilium. The borders of the 
opening into the stomach, which was of considerable size, 
had united, in healing, with the margins of the external 
wound, but the cavity of the stomach was at last sepa- 
rated from the exterior by a fold of mucous membrane, 
which projected from the upper and back part of the 
opening, and closed it like a valve, but could be pushed 
back with the finger. The introduction of any mechanical 
irritant, such as the bulb of a thermometer, into the 
stomach, excited at once the secretion of gastric fluid. 
This could be drawn off with a caoutchouc tube, and could 
often be obtained to the extent of nearly an ounce. The 
introduction of alimentary substances caused a much more 
rapid and abundant secretion of pure gastric fluid than 
the presence of other mechanical irritants did. No in- 
crease of temperature could be detected during the most 
active secretion; the thermometer introduced into the 
stomach always stood at ioo° Fahr., except during mus- 
cular exertion, when the temperature of the. stomach, like 



THE GASTRIC FLUID. 273 

that of other parts of the body, rose one or t\Yo degrees 
higher. 

M. Blondlot, and subsequently M. Bernard, and since 
then, several others, by maintaining fistulous openings into 
the stomachs of dogs, have confirmed most of the facts 
discovered by Dr. Beaumont. And the man St. Martin 
has frequently submitted to renewed experiments on Lis 
stomach by various physiologists. From all these observa- 
tions it appears, that pepper, salt, and other soluble 
stimulants, excite a more rapid discharge of gastric fluid 
than mechanical irritation does ; so do alkalies generally, 
but acids have a contrary efiect. When mechanical irri- 
tation is carried beyond certain limits so as to produce 
pain, the secretion, instead of being more abundant, 
diminishes or ceases entirely, and a ropy mucus is poured 
out instead. Very cold water, or small pieces of ice, at 
first render the mucous membrane pallid, but soon a kind 
of reaction ensues, the membrane becomes turgid with 
blood, and a larger quantity of gastric juice is poured out. 
The application of too much ice is attended by diminution 
in the quantity of fluid secreted, and by consequent re- 
tardation of the process of digestion. The quantity of the 
secretion seems to be influenced also by impressions made 
on the mouth ; for Blondlot found that when sugar was 
introduced into the dog's stomach, either alone, or mixed 
with human saliva, a very small secretion ensued : but 
when the dog had himself masticated and swallowed it, 
the secretion was abundant. 

Dr. Beaumont described the secretion of the human 
stomach as '^ a clear transparent fluid, inodorous, a little 
saltish, and very perceptibly Acid. Its taste is similar to 
that of thin mucilaginous water, slightly acidulated with 
muriatic acid. It is readily diffusible in water, wine, or 
spirits ; slightly effervesces with alkalies ; and is an effec- 
tual solvent of the materia alimentaria. It possesses the 



1 



2/4 DIGESTIOX. 

property of coagulating albumen in an eminent degree ; 
is powerfully antiseptic, checking the putrefaction of meat ; 
and effectually restorative of healthy action, when applied 
to old foetid sores and foul ulcerating surfaces." 

The chemical composition of the gastric juice of the 
human subject has been particularly investigated by 
Schmidt, a favourable case for his doing so occurring in 
the person of a peasant named Catherine Kiitt, aged 35, 
who for three years had had a gastric fistula under the left 
mammary gland, between the cartilages of the ninth and 
tenth ribs. 

The fluid was obtained by putting into the stomach 
some hard indigestible matter, as dry peas, and a little 
water, by which means the stomach was excited to secre- 
tion, at the same time that the matter introduced did 
not complicate the analysis by being digested in the fluid 
secreted. The gastric juice was drawn off through an 
elastic tube inserted into the fistula. 

The fluid thus obtained was acid, limpid, and odourless, 
with a mawkish taste. Its density varied from 1*0022 to 
I '0024. Under the microscope a few cells from the gastric 
glands and some fine granular matter were observable. 

The following table gives the mean of two analyses of 
the above-mentioned fluid ; and arranged by the side of it, 
for purposes of comparison, is an analysis of gastric juice 
from the sheep and dog. 



COMPOSITION OF GASTRIC FLUID. 2/5 



Composition of Gastric Juice. 

Human Sheep's Dog's 

Gastric Juice. Gastric Juice. Gastric Juice. 



Water 


994-40 


986-14 


971-17 


Solid Constituents 


5-59 


13-85 


28-82 




Ferment, Pepsin (with 










a trace of Ammonia) . 


3-19 


4-20 


1 7 'SO 




Hydrochloric Acid 


020 


1-55 


2-70 


dS( 


Chloride of Calcium 


0'o6 


O'll 


1-66 




„ Sodium 


I '46 


436 


3'i4 




„ Potassium . 


055 


1*51 


I -07 




Phosphate of Lime, 










Magnesia, and Iron . 


0-12 


2-09 


273 



In all the above analyses the amount of water given 
must be reckoned as rather too much, inasmuch as a cer- 
tain quantity of saliva was mixed with the gastric fluid. 
The allowance, however, to be made on this account is 
only very small. 

Considerable difference of opinion has existed concern- 
ing the naturo of the free acid contained in the gastric 
juice, chiefly whether it is hydrochloric or lactic. The 
weight of evidence, however, is in favour of free hydro- 
chloric acid, being that to which, in the human subject, the 
acidity of the gastric fluid is mainly due ; although there 
is no doubt that others, as lactic, acetic, butyric, are not 
unfrequently to be found therein. 

The animal matter mentioned in the analysis of the gas- 
tric fluid is named pepsin, from its power in the process 
of digestion. It is an azotised substance, and is best pro- 
cured by digesting portions of the mucous membrane of 
the stomach in cold water, after they have been macerated 
for some time in water at a temperature between 80° and 
100° F. The warm water dissolves various substances as 
weU as some of the pepsin, but the cold water takes up 
little else than pepsin, which, on evaporating the cold 

T 2 



276 DIGESTION. 

solution, is obtained in a greyish-brown viscid fluid. The 
addition of alcohol throws down the pepsin in greyish- 
white flocculi ; and one part of the principle thus prepared, 
if dissolved in even 6o,000 parts of water, wiU digest meat 
and other alimentary substances. 

The digestive power of the gastric fluid is manifested in its 
softening, reducing into pulp, and partially or completely 
dissolving various articles of food placed in it at a tempe- 
rature of from 90° to 100°. This, its peculiar property, 
requires the presence of both the pepsin and the acid j. 
neither of them can digest alone, and when they are 
mixed, either the decomposition of the pepsin, or the 
neutralization of the acid, at once destroys the digestive 
property of the fluid. For the perfection of the process 
also, certain conditions are required, which are aU found 
in the stomach ; namely ( i ), a temperature of about 
100° F. ; (2), such movements as the food is subjected to 
by the muscular actions of the stomach, which bring in 
succession every part of it in contact with the mucous 
membrane, whence the fresh gastric fluid is being secreted ; 
(3), the constant removal of those portions of food which 
are already digested, so that what remains undigested may 
be brought more completely into contact with the solvent 
fluid ; and (4) a state of softness and minute division, such 
as that to which the food is reduced by mastication previous 
to its introduction into the stomach. 

The chief circumstances connected with the mode in 
which the gastric fluid acts upon food during natural diges- 
tion, have been determined by watching its operations 
when removed from the stomach and placed in conditions 
as nearly as possible like those under which it acts while 
within that viscus. The fact that solid food, immersed in 
gastric fluid out of the body, and kept at a temperature of 
about 100°, is gradually converted into a tliick fluid similar 
to chyme, was shown by SpaUanzani, Dr. Stevens, Tiede- 
mann and Gmelin and others. They used the gastric fluid 



DIGESTIVE POWER OF GASTEIC FLUID. 277 

of dogs, obtained by causing the animals to swallow smaU 
pieces of sponge, wbich were subsequently withdrawn, 
soaked with the fluid — and proved nearly as much as the 
latter experiments of the same kind of gastric fluid by 
Blondlot, Bernard, and others. But these need not be 
particularly referred to, while we have the more satisfac- 
tory and instructive observations which Dr. Beaumont 
made with the fluid obtained from the stomach of St. 
Martin. After the man had fasted seventeen hours, 
Dr. Beaumont took one ounce of gastric fluid, put into it a 
solid piece of boiled recently salted beef weighing three 
drachms, and placed the vessel which contained them in a 
water bath heated to 100°. "In forty minutes digestion 
had distinctly commenced over the surface of the meat ; in 
fifty minutes, the fluid had become quite opaque and 
cloudy, the external texture began to separate and become 
loose ; and in sixty minutes chyme began to form. At 
I p.m." (two hours after the commencement of the experi- 
ment) " the cellular texture seemed to be entirely 
destroyed, leaving the muscular fibres loose and xmcon- 
nected, floating about in small fine shreds, very tender and 
soft." In six hours, they were nearly all digested — a few 
fibres only remaining. After the lapse of ten hours, every 
part of the meat was completely digested. The gastric 
juice, which was at first transparent, was now about the 
colour of whey, and deposited a fine sediment of the colour 
of meat. A similar piece of beef "was, at the time of the 
commencement of this experiment, suspended in the 
stomach by means of a thread : at the expiration of the 
first hour it was changed in about the same degree as the 
meat digested artificially; but at the end of the second 
hour, it was completely digested and gone. 

It other experiments. Dr. Beaumont withdrew through 
the opening of the stomach some of the food which had 
been taken twenty minutes previously, and which was 
completely mixed with the gastric juice. He continued 



278 DIGESTION. 

the digestion, wMch had already commenced, by means of 
artificial heat in a water-bath. In a few hours the food 
thus treated was completely chymified ; and the artificial 
seemed in this, as in several other experiments, to be 
exactly similar to, though a Kttle slower than, the natural 
digestion. 

The apparent identity of the process in- and outside of 
the stomach thus manifested, while it shows that we may 
regard digestion as essentially a chemical process, when 
once the gastric fluid is formed, justifies the belief that 
Dr. Beaumont's other experiments with the digestive fluid 
may exactly represent the modifications to which, under 
similar conditions, its action in the stomach would be 
liable. He found that, if the mixture of food and gastric 
fluid were exposed to a temperature of 34° F., the process 
of digestion was completely arrested. In another experi- 
ment, a piece of meat which had been macerated in water 
at a temperature of 100° for several days, tiU it acquired 
a strong putrid odour, lost, on the addition of some fresh 
gastric juice, all signs of putrefaction, and soon began to 
be digested. From other experiments he obtained the 
data for estimates of the degrees of digestibility of various 
articles of food, and of the ways in which the digestion is 
liable to be afiected, to which reference will again be 
made. 

When natural gastric juice cannot be obtained, many 
of these experiments may be performed with an artificial 
digestive fluid, the action of which, probably, very closely 
resembles that of the fluid secreted by the stomach. It is 
made by macerating in water portions of fresh or recently 
dried mucous membrane of the stomach of a pig ^' or other 
omnivorous animal, or of the fourth stomach of the calf, 

* The best portion of the stomach of the pig for this purpose is that 
between the cardiac and pyloric orifices ; the cardiac portion appears 
to furnish the least active digestive fluid. 



I 



ARTIFICIAL DIGESTION. 



279 



and adding to the infusion a few drops of hydrocliloric 
acid — about 3"3 grains to haK an ounce of the mixture, 
according to Schwann. Portions of food placed in such 
fluid, and maintained with it at a temperature of about 
100°, are, in an hour or more, according to the toughness 
of the substance, softened and changed in just the same 
manner as they would be in the stomach. 

The nature of the action by which the mucous mem- 
brane of the stomach and its secretion work these changes 
in organic matter is exceedingly obscure. The action of 
the pepsin may be compared with that of a ferment, which 
at the same time that it undergoes change itself, induces 
certain changes also in the organic matters with which it 
is in contact. Or its mode of action may belong to that 
class of chemical processes termed " catalytic," in which 
a substance excites, by its mere presence, and without 
itself undergoing change as ordinary ferments do, some 
chemical action in the substances with which it is in 
contact. So, for example, spongy platinum, or charcoal, 
placed in a mixture, however voluminous, of oxygen and 
hydrogen, makes them combine to form water ; and 
diastase makes the starch in grains undergo transforma- 
tion, and sugar is produced. And that pepsin acts in 
some such manner appears probable from the very minute 
quantity capable of exerting the peculiar digestive action 
on a large quantity of food, and apparently with little 
diminution in its active power. The process differs from 
ordinary fermentation, it beiug unattended with the for- 
mation of carbonic acid, in not requiring the presence of 
oxygen, and in being unaccompanied by the production of 
new quantities of the active principle, or ferment. It 
agrees with the processes of both fermentation and organic 
catalysis, in that whatever alters the composition of the 
pepsin (such as heat above ioo°, strong alcohol, or strong 
acids), destroys the digestive power of the fluid. 



280 DIGESTION. 

Changes of the Food in the Stomach. 

The general effect of digestion in the stomach is the 
conversion of the food into chyme, a substance of various 
composition according to the nature of the food, yet always 
presenting a characteristic thick, pultaceous, grumous con- 
sistence, with the undigested portions of the food mixed 
in a more fluid substance, and a strong, disagreeable acid 
odour and taste. Its colour depends on the nature of the 
food, or on the admixture of yellow or green bile which 
may, apparently, even in health, pass into the stomach. 

Reduced into such a substance, all the various materials 
of a meal may be mingled together, and near the end of 
the digestive process hardly admit of recognition ; but the 
experiments of artificial digestion, and the examination of 
stomachs with fistulse, have illustrated many of the changes 
through which the chief alimentary principles pass, and 
the times and modes in which they are severally disposed 
of. These must now be traced. 

The readiness with which the gastric fluid acts on the 
several articles of food is, in some measure, determined by 
the state of division, and the tenderness and moisture of 
the substance presented to it. By minute division of the 
food, the extent of surface with which the digestive fluid 
can come in contact is increased, and its action proportion- 
ably accelerated. Tender and moist substances offer less 
resistance to the action of the gastric juice than tough, 
hard, and dry ones do, because they may be thoroughly 
penetrated by it, and thus be attacked not only at the 
surface, but at every part at once. The readiness with 
which a substance is acted upon by the gastric fluid does 
not, however, necessarily imply the degree of its nutritive 
property ; for a substance may be nutritious, yet, on 
account of its toughness and other qualities, hard to 
digest ; and many soft, easily digested substances contain 
comparatively a small amount of nutriment. But for a 



I 



DIGESTION OF FOOD IN THE STOMACH. 28 1 

substance to be nutritive, it must be capable of being 
assimilated to the blood ; and to find its way into tbe 
blood, it must, if insoluble, be digestible by the gastric 
fluid or some other secretion in the intestinal canal. There 
is, therefore, thus far, a necessary connection between the 
digestibility of a substance and its power of affording 
nutriment. 

Those portions of food which are liquid when taken into 
the stomach, or which are easily soluble in the fluids 
therein, are probably at once absorbed by the blood- 
vessels in the mucous membrane of the stomach. Magen- 
die's experiments, and better still, those of Dr. Beaumont, 
have proved this quick absorption of water, wine, weak 
saline solutions, and the like ; that they are absorbed 
without manifest change by the digestive fluid, and that, 
generally, the water of such liquid food as soups is 
absorbed at once, so that the substances suspended in it 
are concentrated into a thicker material, like the chyme 
from solid food, before the digestive fluid acts upon them. 

The action of the gastric fluid on the several kinds of solid 
food has been studied in various ways. In the earliest 
experiments, perforated metallic and glass tubes, fiUed 
with the alimentary substances, were introduced into the 
stomachs of animals, and after the lapse of a certain time 
withdrawn, to observe the condition of the contained sub- 
stances ; but such experiments are fallacious, because 
gastric fluid has not ready access to the food. A better 
method was practised in a series of experiments by Tiede- 
mann and Gmelin, who fed dogs with different substances, 
and kiUed them in a certain number of hours afterwards. 
But the results they obtained are of less interest than 
those of the experiments of Dr. Beaumont on his patient, 
St. Martin, and of Dr. Gosse, who had the power of 
vomiting at will. 

Dr. Beaumont's observations show, that the process of 
digestion in the stomach, during health, takes place so 



2«2 DIGESTION, 

rapidly, that a full meal, consisting of animal and vege- 
table substances, may nearly all be converted into chyme 
in about an hour, and the stomach left empty in two hours 
and a half. The details of two days' experiments will be 
sufficient examples : — 

Exp. 42. — April 7th, 8 a.m. St. Martin breakfasted on 
three hard-boiled eggs, pancakes, and coffee. At half-past 
eight a' clock, Dr. Beaumont examined the stomach, and 
found a heterogeneous mixture of the several articles 

slightly digested At a quartar past ten, no part of 

the breakfast remained in the stomach. 

Exp. 43. — At eleven o'clock the same day, he ate two 
roasted eggs and three ripe apples. In half an hour they 
were in an incipient state of digestion ; and a quarter] past 
twelve no vestige of them remained. 

Exp. 44. — At two o'clock P.M. the same day, he dined 
on roasted pig and vegetables. At three o'clock they were 
half chymified, and at half-past four nothing remained but 
a very little gastric juice. 

Again, Exp. 46. — April 9th. At three o'clock p.m. he 
dined on boiled dried codfish, potatoes, parsnips, bread, 
and drawn butter. At half-past three o'clock examined, 
and took out a portion about half digested ; the potatoes 
the least so. The fish was broken down into small 
filaments ; the bread and parsnips were not to be dis- 
tinguished. At four o'clock, examined another portion. 
Very few particles of fish remained entire. Some of the 
few potatoes were distinctly to be seen. At half-past four 
o'clock, he took out and examined another portion ; all 
completely chymified. At five o'clock stomach empty. 

Many circumstances besides the nature of the food are 
apt to influence the process of chymification. Among them 
are, the quantity of food taken; the stomach should be 
fairly fiUed, not distended : the time that has elapsed since 
the last meal, which should be at least enough for the 
stomach to be quite clear of food : the amount of exercise 



DIGESTION m THE STOMACH. 285 

previous and subsequent to the meal, gentle exercise being 
favourable, over- exertion iujurious to digestion ; the state 
of mind — tranquillity of temper being apparently essential 
to a quick and due digestion : the bodily health : the state 
of the weather. But under ordinary circumstances, from 
three to four hours may be taken as the average time 
occupied by the digestion of a meal in the stomach. 

Dr. Beaumont constructed a table showing the times 
required for the digestion of aU usual articles of food in 
St. Martin's stomach, and in his gastric fluid taken from 
the stomach. Among the substances most quickly digested 
were rice and tripe, both of which were chymified in an 
hour; eggs, salmon, trout, apples, and venison, were 
digested in an hour and a half; tapioca, barley, milk, 
liver, fish, in two hours; turkey, lamb, potatoes, pig, in 
two hours and a half; beef and mutton required from 
three hours to three and a half, and both were more 
digestible than veal ; fowls were like mutton in their degree 
of digestibility. Animal substances were, in general, con- 
verted into chyme more rapidly than vegetables. 

Dr. Beaumont's experiments were all made on ordinary 
articles of food. A minuter examination of the changes 
produced by gastric digestion on various tissues has been 
made by Dr. Rawitz, who examined microscopically the 
product of the artificial digestion of difi'erent kinds of 
food, and the contents of the faeces after eating the same 
kinds of food. The general results of his examinations, 
as regards animal food, show that muscular tissue breaks 
up into its constituent fasciculi, and that these again are 
divided transversely ; gradually the transverse striae become 
indistinct, and then disappear ; and finally, the sarcolemma 
seems to be dissolved, and no trace of the tissue can be 
found in the chyme, except a few fragments of fibres. 
These changes ensue most rapidly in the flesh of fijsh and 
hares, less rapidly in that of poultry and other animals. 
The cells of cartilage and fibro-cartilage, except those of fish, 



284 DIGESTION. 

pass unchanged through the stomach and intestines, and 
may be foimd in the faeces. The interstitial tissues of these 
structures are converted into pulpy textureless substances 
in the artificial digestive fluid, and are not discoverable in 
the faeces. Elastic fibres are unchanged in the digestive 
fluid. Fat-cells are sometimes found quite unaltered in the 
faeces : and crystals of cholesterin may usually be obtained 
from faeces, especially after the use of pork fat. 

As regards vegetable substances. Dr. Rawitz states, that 
he frequently found large quantities of cell-membranes un- 
changed in the faeces ; also starch-cells, commonly ^deprived 
of only part of their contents. The green colouring prin- 
ciple, chlorophyll, was usually unchanged. The walls of 
the sap-vessels and spiral vessels were quite unaltered by 
the digestive fluid, and were usually found in large 
quantities in the faeces; their contents, probaby, were 
-removed. 

From these experiments, we may understand ^e structural 
changes which the chief alimentary substances undergo in 
their conversion into chyme ; and the proportions of each 
which are not reducible to chyme, nor capable of any 
further act of digestion. The chemical changes undergone 
in and by the proximate principles are less easily traced. 

Of the albuminous principles, some, as the casein of milk, 
are coagulated by the acid of the gastric fluid ; and thus, 
before they are digested, come into the condition of the 
other solid principles of the food. These, including solid 
albumen and fibrin, in the same proportion that they are 
broken up and anatomically disorganized by the gastric 
fluid, appear to be reduced or lowered in their chemical 
composition. This chemical change is probably produced, 
as suggested by Dr. Prout, by the principles entering into 
combination with water. It is suflicient to conceal nearly 
aU their characteristic properties ; the albumen is rendered 
scarcely coagulable by heat; the gelatin, even when its 
solution is evaporated, does not congeal in cooling; the 



DIGESTION IN THE STOMACH. 285 

fibrin and casein cannot be found by their characteristic 
tests. It would seem, indeed, that all these various sub- / 
stances are converted into one and the same principle, a 1 
low form of albumen, not precipitable by nitric acid or heat, \ 
and now generally termed alb uminose or peptone^ from which, \ 
after being absorbed, they are again raised, in the elabora- 
tion of the blood, to which they are ultimately assimilated. 

The change of molecular constitution suffered by the 
albuminous parts of the food, in consequence of the action 
of the gastric juice, has an important relation to their 
absorption by the blood-vessels of the stomach. From the 
condition of ' colloids,' or substances, so named by Profes- 
sor Graham, which are absorbed with extreme difficulty, 
they appear, from experiments of Funke, to assume to a 
great degree the character of ' crystalloids,' which can 
pass through animal membranes with ease.^^ 

Whatever be the mode in which the gastric secretion 
affects these principles, it, or something like it, appears 
essential, in order that they may be assimilated to the 
blood and tissues. For, when Bernard and Barreswil in- 
jected albumtjn dissolved in water into the jugular veins 
of dogs, they always, in about three hours after, found it 
in the urine. But if, previous to injection, it was mixed 
with gastric fluid, no trace of it could be detected in the 
urine. The influence of the liver seems to be almost as 
efficacious as that of the gastric fluid, in rendering albu- 
men assimilable ; for Bernard found that, if diluted egg- 
albumen, unmixed with gastric fluid, is injected into the 
portal vein, it no longer makes its appearance in the urine, 
and is, therefore, no doubt, assimilated by the blood. 

, Probably, most of the albuminose, with other soluble ' 
and fluid materials, is absorbed directly from the stomach 
by the minute blood-vessels with which the mucous mem- 
brane is so abundantly supplied. 

* These terms will be further explained and illustrated in the Chapter 
on Absorption. 



286 DIGESTION. 

The saccharine including the amylaceous principles are at 
first, probably, only mechanically separated from the vege- 
table substances within which they are contained, by the 
action of the gastric fluid. The soluble portions, viz., 
dextrin and sugar, are probably at once absorbed. The 
insoluble ones, viz., starch and lignin, (or some parts of 
them) are rendered soluble and capable of absorption, by 
being converted into dextrin or grape-sugar. It is pro- 
bable that this change is carried on to some extent in 
the stomach ; but this conversion of starch into sugar is 
effected, not by the gastric fluid, but by the saliva intro- 
duced with the food, or subsequently swallowed. The 
transformation of starch is continued in the intestinal 
canal, as will be shown, by the secretion of the pancreas, 
and perhaps by that of the intestinal glands and mucous 
membrane. The power of digesting uncooked starch is, 
however, very limited in man and Camivora, for when 
starch has been taken raw, as in com and rice, large 
quantities of the granules are passed unaltered with the 
excrements. Cooking, by expanding or bursting the 
envelopes of the granules, renders their interior more 
amenable to the action of the digestive organs ; and the 
abundant nutriment furnished by bread, and the large 
proportion that is absorbed of the weight consumed, afibrd 
proof of the completeness of their power to make its starch 
soluble and prepare it for absorption. 

Of the oleaginous principles, — as to their changes in the 
stomach, no more can be said than that they appear to be 
reduced to minute particles, and pass into the intestines 
mingled with the other constituents of the chyme. In the 
case of the solid fats, this efl'ect is probably produced by 
the solvent action of the gastric juice on the areolar tissue, 
albuminous cell-walls, «&:c., w^hich enter into their com- 
position, and by the solution of which the true fat is able 
to mingle more uniformly with the other constituents of 
the chyme. Being further changed in the intestinal canal, 
fat is rendered capable of absorption by the lacteals. 



MOVEMENTS IN THE STOMACH. 287 

Movements of the Stomach. 

It has been already said, that the gastric fluid is assisted 
in accomplishing its share in digestion by the movements 
of the stomach. In granivorous birds, for example, the 
contraction of the strong muscular gizzard affords a neces- 
sary aid to digestion, by grinding and triturating the 
hard seeds which constitute part of the food. But in the 
stomachs of man and Mammalia the motions of the mus- 
cular coat are too feeble to exercise any such mechanical 
force on the food ; neither are they needed, for mastication 
has already done the mechanical work of a gizzard j and 
the experiments of Reaumur and Spallanzani have demon- 
strated that substances enclosed in perforated tubes, and 
consequently protected from mechanical influence, are yet 
digested. 

The normal actions of the muscular fibres of the human 
stomach appear to have a three-fold purpose; first, to 
adapt the stomach to the quantity of food in it, so that its 
walls may be in contact with the food on all sides, and, at 
the same time, may exercise a certain amount of com- 
pression upoix it; secondly, to keep the orifices of the 
stomach closed until the food is digested ; and, thirdly, to 
perform certain peristaltic movements, whereby the food, 
as it becomes chymified, is gradually propelled towards, 
and ultimately through, the pylorus. In accomplishing 
this latter end, the movements without doubt materially 
contribute towards effecting a thorough intermingling of 
the food and the gastric fluid. 

When digestion is not going on, the stomach is uniformly 
contracted, its orifices not more firmly than the rest of its 
walls ; but, if examined shortly after the introduction of 
food, it is found closely encircling its contents, and its ori- 
fices are firmly closed like sphincters. The cardiac orifice, 
every time food is swallowed, opens to admit its passage 
to the stomach, and immediately again closes. The pyloric 
orifice, during the first part of gastric digestion, is usually 



288 DIGESTION. 

so completely closed, that even when the stomach is sepa- 
rated from the intestines, none of its contents escape. But 
towards the termination of the digestive process, the 
pylorus seems to offer less resistance to the passage of 
substances from the stomach ; first it yields to allow the 
successively digested portions to go through it ; and then 
it allows the transit of even undigested substances. 

From the observations of Dr. Beaumont on the man St. 
Martin, it appears that food, so soon as it enters the 
stomach, is subjected to a kind of peristaltic action of the 
muscular coat, whereby the digested portions are gradually 
approximated towards the pylorus. The movements were 
observed to increase in rapidity as the process of chymifica- 
tion advanced, and were continued until it was completed. 

The contraction of the fibres situated towards the pyloric 
end of the stomach seems to be more energetic and more 
decidedly peristaltic than those of the cardiac portion. 
Thus, Dr. Beaumont found that when the bulb of the 
thermometer was placed about three inches from the 
pylorus, it was tightly embraced from time to time and 
drawn towards the pyloric orifice for a distance of three or 
four inches. The object of this movement appears to be, 
as just said, to carry the food towards the pylorus as fast 
as it is formed into chyme, and to propel the chyme into 
the duodenum; the undigested portions of food being 
kept back until they are also reduced into chyme, or until 
all that is digestible has passed out. The action of these 
fibres is often seen in the contracted state of the pyloric 
portion of the fetomach after death, when it alone is con- 
tracted and firm, while the cardiac portion forms a dilated 
sac. Sometimes, by a predominant action of strong circular 
fibres placed between the cardia and pylorus, the two por- 
tions, or ends as they are called, of the stomach, are separated 
from each other by a kind of hour-glass contraction. 

The interesting researches of Dr. Brinton have clearly 
established that, by means of this peristaltic action of the 



MOVEMENTS OF THE STOMACH. 289 

muscular coats of the stomach, not merely is chymified 
food gradually propelled through the pylorus, but a kind 
of double current is continually kept up among the con- 
tents of the stomach, the circumferential parts of the mass 
being gradually moved onward towards the pylorus by 
the peristaltic contraction of the muscular fibres, while the 
central portions are propelled in the opposite direction, 
namely, towards the cardiac orifice ; in this way is kept up 
a constant circulation of the contents of the viscus, highly 
conducive to their free mixture with the gastric fluid and 
to their ready digestion. 

These actions of the stomach are peculiar to it and inde- 
pendent. But it is, also, adapted to act in concert with 
the abdominal muscles, in certain circumstances which can 
hardly be called abnormal, as in vomiting and eructation. 
It has indeed been frequently stated that the stomach 
itself is quite passive during vomiting, and that the ex- 
pulsion of its contents is effected solely by the pressure 
exerted upon it when the capacity of the abdomen is 
diminished by the contraction of the diaphragm, and sub- 
sequently of the abdominal muscles. The experiments 
and observations, however, which are supposed to confirm 
this statement, only show that the contraction of the abdo- 
minal muscles alone is sufficient to expel matters from an 
unresisting bag through the oesophagus ; and that, under 
very abnormal circumstances, the stomach, by itself, cannot 
or rather does not expel its contents. They by no means 
show that in ordinary vomiting the stomach is passive ; 
and, on the other hand, there are good reasons for believing 
the contrary. 

It is true that facts are wanting to demonstrate with 
certainty this action of the stomach in vomiting ; but some 
of the cases of fistulous opening into the organ appear 
to support the beKef that it does take place ;^' and the 

* A collection of cases of fistulous communication with the stomach, 
through the abdominal x^arietes, has heen given by Dr. Murchison in 
vol. xli. of the Medico-Chirurgical Transactions. ir 



290 



DIGESTIO]S\ 



analogy of the case of the stomach with that of the other 
hollow viscera, as the rectum aad bladder, may be also 
cited in confirmation. 

Besides the influence which it may thus have by its con- 
traction, the stomach also essentially contributes to the act 
of vomiting, by the contraction of its pyloric orifice at the 
same time that the oblique fibres around the cardiac orifice 
are relaxed. For, until the relaxation of these fibres, no 
vomiting can ensue ; when contracted, they can as well 
resist all the force of the contracting abdominal and other 
muscles, as the muscles by which the glottis is closed can 
resist the same force in the act of straining. Doubtless 
we may refer many of the acts of retching and ineffectual 
attempts to vomit, to the want of concord between the 
relaxation of these muscles and the contraction of the 
others. 

The muscles with which the stomach co-operates in con- 
traction during vomiting, are chiefly and primarily those 
of the abdomen ; the diaphragm also acts, but not as the 
muscles of the abdominal walls do. They contract and 
compress the stomach more and more towards the back 
and upper parts of the diaphragm ; and the diaphragm 
(which is usually drawn down in the deep inspiration that 
precedes each act of vomiting) holds itself fixed in contrac- 
tion, and presents an unyielding surface against which the 
stomach may be pressed. It is enabled to act thus, and 
probably only thus, because the inspiration which precedes 
the act of vomiting is terminated by the closure of the glottis ; 
after which the diaphragm can neither descend further, 
except by expanding the air in the lungs, nor, except by 
compressing the air, ascend again until, the act of vomiting 
having ceased, the glottis is opened again (see diagram, 
p. 231; see also p. 233). 

Some persons possess the power of vomiting at will, 
without applying any undue irritation to the stomach, but 
simply by a voluntary effort. It seems also, that this 
power may be acquired by those who do not naturally 



UttAA^ 



HUNGER AND THIRST. 29 1 

possess it, and by continual practice may become a babit. 

There are cases also of rare occurrence in wbicb persons] 

habitually swallow their food hastily, and nearly unmasti- 

cated, and then at their leisure regurgitate it, piece by 

piece, into their mouth, remasticate, and again swallow it, ITTN e.^ 

exactly as is done by the ruminant order of Mammalia. 

Influence of the Nervous System on Gastric Digestion. 

This influence is manifold ; and is evidenced, ist, in the 
sensations which induce to the taking of food ; 2nd, in the 
secretion of the gastric fluid ; ^rd, in the movements of the 
food in and from the stomach. 

The sensation of hunger is manifested in consequence of 
deficiency of food in the system. The mind refers the 
sensation to the stomach ; yet since the sensation is relieved 
bj^ the introduction of food either into the stomach itself, 
or into the blood through other channels than the stomach, 
it would appear not to depend on the state of the stomach 
alone. This view is confirmed by the fact, that the divi- 
sion of both pneumogastric nerves, which are the principal 
channels by v< hich the mind is cognisant of the condition 
of the stomach, does not appear to allay the sensations of 
hunger. 

But that the stomach has some share in this sensation 
is proved by the relief afforded, though only temporarily, 
by the introduction of even non-alimentary substances into 
this organ. It may, therefore, be said that the sensation 
of hunger is derived from the system generally, but chiefly 
from the condition of the stomach, the nerves of which, 
we may suppose, are more affected by the state of the in- 
sufficiently replenished blood than those of other organs 
are. 

The sensation of thirst, indicating the want of fluid, is 
referred to the fauces, although, as in hunger, this is 
merely the local declaration of a general condition existing 
in the system. For thirst is relieved for only a very short 

u 2 



292. DIGESTIOI^. 

time by moistening the dry fauces ; but may be relieved 
completely by the introduction of liquids into the blood, 
either through the stomach, or by injections into the 
blood-vessels, or by absorption from the surface of the 
skin or the intestines. The sensation of thirst is per- 
ceived most naturally whenever there is a disproportion- 
ately small quantity of water in the blood : as well, 
therefore, when water has been abstracted from the blood, 
as when saline or any solid inatters have been abundantly 
added to it. We can express the fact (even if it be not 
an explanation of it), by saying that the nerves of the 
mouth and fauces, through which the sense of thirst is 
chiefly derived, are more sensitive to this condition of the 
blood than other nerves are. And the cases of hunger 
and thirst are not the only ones in which the mind derives, 
from certain organs, a peculiar predominant sensation of 
some condition affecting the whole body. Thus, the sensa- 
tion of the " necessity of breathing," is referred especially 
to the lungs ; but, as Volkmann's experiments show, it 
depends on the condition of the blood, which circulates 
everywhere, and is felt even after the lungs of animals 
are removed ; for they continue, even then, to gasp and 
manifest the sensation of want of breath. And, as with 
respiration when the lungs are removed, the mind may 
still feel the body's want of breath ; so in hunger and 
thirst, even when the stomach has been filled with innu- 
tritions substances, or the pneumogastric nerves have 
been divided, and the mouth and fauces are kept moist, 
the mind is still aware, by the more obscure sensations in 
other parts, of the whole body's need of food and 
water. 

The influence of tJie nervous system on the secretion of gastric 
fluid, is shown plainly enough in the influence of the mind 
upon digestion in the stomach ; and is, in this regard, well 
illustrated by several of Dr. Beaumont's obocrvations. 
M. Bernard also, watching the act of gastric digestion in 



INFLUENCE OF THE NERVOUS SYSTEM. 



293 



dogs which, had fistulous openings into their stomachs, 
saw that on the instant of dividing their pneumogastric 
nerves, the process of digestion was stopped, and the 
mucuous membrane of the stomach, previously turgid with 
blood, became pale, and ceased to secrete. These, how- 
ever, and the like experiments showing the instant effect 
of division of the pneumogastric nerves, may prove no 
more than the effect of a severe shock, and the fact that 
influences affecting digestion may be conveyed to the 
stomach through those nerves. From other experiments 
it may be gathered, that although, as in M. Bernard's, 
the division of both pneumogastric nerves always tem- 
porarily suspends the secretion of gastric fluid, and so 
arrests the process of digestion, and is occasionally followed 
by death from inanition ; yet the digestive powers of the 
stomach may be completely restored after the operation, 
and the formation of chyme and the nutrition of the animal 
may be carried on almost as perfectly as in health. 

In thirty experiments on ^Mammalia, which M. Wem- 
Scheldt performed under Miiller's direction, not the least 
difference could be perceived in the action of narcotic 
poisons introduced into the stomach, whether the pneu- 
mogastric had been divided on both sides or not, provided 
the animals were of the same species and size. It appears, 
however, that such poisons as are capable of being 
rendered inert by the action of the gastric fluid, may, if 
taken into the stomach shortly after division of both 
pneumogastric nerves, produce their poisonous effects ; 
in consequence, apparently, of the temporary suspension 
of the secretion of gastric fluid. Thus, in one of his 
experiments, M. Bernard gave to each of two dogs, in one 
of which he had divided the pneumogastric nerves, a 
dose of emulsine, and half an hour afterwards a dose of 
amygdaline, substances which are innocent alone, but 
when mixed, produce hydrocyanic acid. The dog whose 
nerves were cut, died in a quarter of an hour, the sub- 



294 DIGESTION. 

stances being absorbed unaltered and mixing in the blood ; 
in the other, the emulsine was decomposed by the gastric 
fluid before the amygdaline was administered; therefore, 
hydrocyanic acid was not formed in the blood, and the dog 
survived. 

The influence of the pneumogastric nerves over the 
secretion of gastric fluid has been of late even more de- 
cidedly shown by M. Bernard, who found that galvanic 
stimulus of these nerves excited an active secretion of the 
fluid, while a like stimulus applied to the sympathetic 
nerves issuing^from the semilunar ganglia, caused a dimi- 
nution and even complete arrest of the secretion. 

The influence of the nervous system on the movements of the 
stomach has been often seen in the retardation or arrest 
of these movements after division of the pneumogastric 
nerves. The results of irritating the same nerves were 
ambiguous; but the experiments of Longet and Bischofi" 
have shown that the different results depended on whether 
the stomach were digesting or not at the time of the experi- 
ment. In the act of digestion, the nervous system of the 
stomach appears to participate in the excitement which 
prevails through the rest of its organization, and a stimulus 
applied to the pneumogastric nerves is felt intensely, and 
active movements of the muscular fibres of the stomach 
foUow; but in the inaction of fasting, the same stimulus^ 
produces no effect. So, while the stomach is digesting, 
the pylorus is too irritable to allow anything but chyme to 
pass ; but when digestion is ended, the undigested parts of 
the food, and even large bodies, coins, and the like, may 
pass through it. 

Digestion of the Stomach after Death. 

If an animal die during the process of gastric digestion, 
and when, therefore, a quantity of gastric juice is present 
in the interior of the stomach, the walls of this organ itself 



POST-MOETEM DIGESTION. 295 

are frequently themselves acted on by their own secretion, 
and to such an extent, that a perforation of considerable 
size may be produced, and the contents of the stomach 
may in part escape into the cavity of the abdomen. 
This phenomenon is not unfrequently observed in post- 
mortem examinations of the human body ; but, as Dr. 
Pavy observes, the effect may be rendered, by experi- 
ment, more strikingly manifest. '' If, for instance," 
he remarks, " an animal, as a rabbit, be killed at a 
period of digestion, and afterwards exposed to artificial 
warmth to prevent its temperature from falling, not 
only the stomach, but many of the surrounding parts 
wiU be found to have been dissolved. With a rabbit 
killed in the evening, and placed in a warm situation (ioo° 
to] 110° Fahr.) during the night, I have seen in the 
morning, the stomach, diaphragm, part of the liver, and 
lungs, and the intercostal muscles of the side upon which 
the animal was laid all digested away, with the muscles 
and skin of the neck and upper extremity on the same 
side also in a semi-digested state." 

From these facts, it becomes an interesting question why, 
during life, the stomach is free from liability to injury 
from a secretion, which, after death, is capable of such 
destructive effects ? John Hunter, who particularly drew 
attention to the phenomena of post-mortem digestion, ex- 
plained the immunity from injury of the living stomach, 
by referring it to the protective influence of the ''vital 
principle." But this dictum has been called in question by 
subsequent observers. It is, indeed, rather a statement 
of a fact, than an explanation of its cause. It must be 
confessed, however, that no entirely satisfactory theory has 
been yet stated as a substitute. 

It is only necessary to refer to the idea of Bernard, that 
the living stomach finds protection from its secretion in the 
presence of epithelium and mucus, which are constantly 
renewed in the same degree that they are constantly dis- 



296 DIGESTIOI^. 

solved, in order to remark that this theory has been 
disproved by experiments of Pavy's, in which the mucus 
membrane of the stomachs of dogs was dissected off for a 
small space, and, on killing the animals some days after- 
wards, no sign of digestion of the stomach was visible. 
''Upon one occasion, after removing the mucous mem- 
brane and exposing the muscular fibres over a space of 
about an inch and a half in diameter, the animal was 
allowed to live for ten days. It ate food every day, and 
seemed scarcely affected by the operation. Life was des- 
troyed whilst digestion was being carried on, and the lesion 
in the stomach was found very nearly repaired : new matter 
had been deposited in the place of what had been removed, 
and the denuded spot had contracted to much less than 
its original dimensions." 

Dr. Pavy believes that the natural alkilinity of the 
blood, which circulates so freely during life in the walls of 
the stomach, is sufficient to neutralize the acidity of the 
gastric juice, were it, so to speak, to make an attempt at 
digesting parts with which it has no business ; and as may 
be gathered from what has been previously said (p. 283), 
the neutralization of the acidity of the gastric secretion is 
quite sufficient to destroy its digestive powers. He also 
very ingeniously argues that this very alkilinity must, from' 
the conditions of the circulation naturally existing in the 
walls of the stomach, be increased in proportion to the 
need of its protective influence. ''In the arrangement of 
the vascular supply," he remarks "a doubly effective 
barrier is, as it were, provided. The vessels pass from 
below upwards towards the surface : capillaries having 
this direction ramify between the tubules by which the 
acid of the gastric juice is secreted ; and being separated 
by secretion below, must leave the blood that is proceeding 
upwards correspondingly increased in alkilinity ; and thus, 
at the period when the largest amount of acid is flowing 
into the stomach, and the greatest protection is required, 



DIGESTION IX THE INTESTINES. 



>97 



tlien is tlie provision afforded in its highest state of 
efficiency." 

Dr. Pavy's theory is the best and most ingenious hitherto 
framed in connection with this subject ; but the experi- 
ments adduced in its favour are open to many objections, 
and afford only a negative support to the conclusions they 
are intended to prove. The matter, therefore, can scarcely 
be considered finally settled. 

DIGESTION IN THE INTESTINES. 

The intestinal canal is divided into two chief portions, 
named, from their differences in diameter, the small and 
large intestine. These are continuous with each other, and 
communicate by means of an opening guarded by a valve, 
the ileo-ccecal valve, which allows the passage of the pro- 
ducts of digestion from the small into the large bowel, but 
not, under ordinary circumstances, in the opposite direction. 

The structure and functions of each organ or tissue con- 
cerned in intestinal digestion will be first described in 
detail, and afterwards a summary will be given of the 
changes which the food undergoes in its passage through 
the intestines, 1st, from the pylorus to the ileo-c8ecal valve ; 
and, 2nd, from the ileo-csecal valve to the anus. 

Structure and Secretions of the Small Intestine. 

I The small intestine, the average length of which in an 
f adult is about twenty feet, has been divided, for conve- 
nience of description, into three portions, viz., the duo- 
denum, which extends for eight or ten inches beyond the 
pylorus ; the jejunum, which occupies two-fifths, and the 
ileum, which occupies three-fifths of the rest of the canal. 

The small intestine, like the stomach, is constructed of 
three principal coats, viz., the serous, muscular, and 
mucous. The serous coat, formed by the visceral layer of 
the peritoneum, need not be here specially described. The 
fibres of the muscular coat of the small intestine are ar- 
ranged in two layers ; those of the outer layer being 



298 



DIGESTION. 



disposed longitudinally ; those of the inner layer trans- 
versely, or in portions of circles encompassing the canal. 
They are composed of the iinstriped kind of muscular fibre. 
Between the mucous and muscular coats, there is a layer 
of submucous tissue, in which numerous blood-vessels and a 
rich plexus of nerves and ganglia are imbedded (Meissner). 
The mucous memhrane is the most important coat in 

relation to the function of 
digestion. The following 
structures which enter into 
the composition may be 
now successively described; 
— the valvulcp. conniventes ; 
the villi ; and the glands. 
The general structure of the 
mucous membrane of the 
intestines resembles that 
of the stomach (p. 266), 
and, like it, is lined on its 
inner surface by columnar 
LympJioid or Hetiform tissue [(fig. 72) enters 
largely into its construction ; and on its deep surface is a 
layer of the muscularis mucosm (p. ay6).-* 2^7 ( 

Valvules Conniventes. ' 

The valvulfe conniventes commence in the duodenum, 
about one or two inches beyond the pylorus, and becoming 
larger and more numerous immediately beyond the en- 
trance of the bile-duct, continue thickly arranged and well 
developed throughout the jejunum ; then, gradually 
diminishing in size and number, they cease near the 




epithelium. 



* Fig. 72. The figure represents a cross section of a small fragment of 
the mucous membrane, including one entire crypt of Lieberkuhn and 
parts of several others : a, cavity of the tubular glands or crypts ; 5, one 
of the lining epithelial cells ; c, the Ijonphoid or retiform spaces, of 
which some are empty, and others occupied by lymph cells, as at c?. 



THE VALVULiE CONXIVENTES. 



299 



Fig. 73. 



middle of the ileum. In structure they are formed by a 
doubling inwards of the mucous membrane, the crescentic, 
nearly circular, folds thus formed being arranging trans- 
versely with regard to the axis of the intestine, and each 
individual fold seldom extending around more than 1^ or f 
of the bowel's circumference. Unlike the rugse in the 
stomach, they do not disappear on distension. Only an 
imperfect notion of their natural position and function can 
be obtained by looking at them after the intestine has been 
laid open in the usual manner. To understand them 
aright, a piece of gut should be distended either with air 
or alcohol, and not opened until the tissues have become 
hardened. On then making a section, it may be seen that 
instead of disappearing, as the rugae in the stomach wotdd 
under similar circumstances, they stand out at right angles 
to the general surface of the mucous 
membrane (fig. 73 )• Their functions 
are probably these — Besides (l) offer- 
ing a largely increased surface for 
secretion and absorption, they proba- 
bly (2) prevent the too rapid passage 
of the very liquid products of gastric 
digestion, immediately after their es- 
cape from the stomach, and (3), by 
their projection, and consequent inter- 
ference with an uniform and untrou- 
bled current of the intestinal contents, 
probably assist in the more perfect 
mingling of the latter with the secre- 
tions poured out to act on them. 

Glands of the Small Intestine, — The glands are of three 
principal kinds, named after their describers, the glands of 
Lieberkiihn, of Peyer, and of Brunn. The glands or fol- 

* Fig, 73. Piece of small intestine Qn-eviously distended and hardened 
by alcohol) laid open to show the normal position of the valvulse con- 
niventes. 




30O DIGESTION. 

Ucles 0^ Lieherliulm are simple tubular depressions of 

the intestinal mucous membrane, tbickly distributed over 

the whole surface both of the large and small 

f't'e-oXt ii^testines. In the small intestine they are visible 

v^fco.^n ^^j^ ^.^^ ^j^^ ^.^ ^£ ^ lens; and their orifices 

appear as minute dots scattered between the villi. 
They are larger in the large intestine, and 
increase in size the nearer they approach the anal 
end of the intestinal tube ; and in the rectum their 
orifices may be visible to the naked eye. In 
length they vary from -^ to -pV of a line. Each 
tubule (fig. 74) is constructed of the same essential 
parts as the intestinal mucous membrane, viz., 
a fine structureless membrana propria, or base- 
ment membrane, a layer of cylindrical epithelium 
lining it and capillary blood-vessels covering its exterior. 
Their contents appear to vary, even in health ; the varieties 
being dependent, probably, on the period of time in rela- 
tion to digestion at which they are examined. At the 
bottom of the follicle, the contents usually consist of a 
granular material, in which a few cytoblasts or nuclei 
are imbedded ; these cytoblasts, as they ascend towards 
the surface, are supposed to be gradually developed into 
nucleated cells, some of which are discharged into the 
intestinal cavity. The purpose served by the material 
secreted by these glands is still doubtful. Their large 
number and the extent of surface occupied by them, seem, 
however, to indicate that they are concerned in other and 
higher offices than the mere production of fluid to moisten 
the surface of the mucous membrane, although, doubtless, 
this is one of their functions. 

The glands of Peijer occur exclusively in the small intes- 
tine. They are found in greatest abundance in the lower 
part of the ileum near to the ileo-cascal valve. They are 

* Fig. 74. A gland of Lieberkiilin. 



TEYER'S GLAXDS. 



301 



met with in two conditions, viz., either scattered singly, 
in which case they are termed glandulcB solitarice, or aggre- ! 
gated in groups varying from one to three inches in length 
and about half-an-inch in width, chiefly of an oval form, 
their long axis parallel with that of the intestine. In this 
state, they are named glandida agminatcB, the groups being 
commonly called Peyer's patches (fig. 75). The latter are 
placed almost always opposite the attachment of the 
mesentery. In structure, and probably in function, there 
is no essential difference between the solitary glands and 

Fig. 75.* 




the individual bodies of which each group or patch is 
made up ; but the surface of the solitary glands (fig. 76) is 
beset with villi, from which those forming the agminate 
patches (fig. 77) are usually free. In the condition in 
which they have been most commonly examined, each 
gland apppears as a circular opaque-white sacculus, from 
half a line to a line in diameter, and, according to the 
degree in which it is developed, either sunk beneath, or 
more or less prominently raised on, the surface of a 
depression or fossa in the mucous membrane. Each gland 



* Fig. 75. Agminate folHcles, or Peyer's faich, in a state of disten- 
sion : magnified about 5 diameters (after Boelmi). 



302 



DIGESTIOX. 



is surrounded by openings like those of Lieberkiihn^s 
follicles (see fig. 77) except that they are more elongated ; 
and the direction of the long diameter of each opening is 
such that the whole produce a radiated appearance around 
the white sacciilus. These openings appear to belong to 
tubules identical with Lieberkiihn's foUicles : they have no 
communication with the sacculus, and none of its contents 
escape through them on pressure. Neither can any 



\ 



Fig. 77.t 



Fig. 76.* 





permanent opening be detected in the sacculus or Peyer*s 
gland itself (see fig. y2>). 

Each gland is an imperfectly closed sac or follicle formed 
•of a tolerably firm membranous capsule of fine connective 
tissue, imbedded in a rich plexus of minute blood-vessels, 
many fine branches from which pass through the capsule 
and enter, chiefly loopwise, the interior of the follicle 
{fig. 79). Entering into the formation of the sacculus, 



* Fig. 76. Solitary gland of small intestine (after Boelim). 

+ Fig. 77. Part of a patch of the so-called Peyer's glands magnified, 
showing the various forms of the sacculi, mth their zone of foramina. 
The rest of the membrane marked with Lieberkiihn's follicles, and 
sprinkled with villi (after Boehm). 



PEYER'S GLANDS. 303 

moreover, and forming a stroma or supporting framework 
throughout its interior, is lymphoid or adenoid tissue (fig. 72), 
continuous with that which forms a great part of the mucous 
membrane outside it. The contents of each sac consist of a 
pale greyish opalescent pulp, formed of albuminous and fatty- 
matter, and a multitude of nucleated corpuscles of various 
sizes, resembling exactly those found in lymphatic glands. 

The real office of these Peyerian glands or follicles is still 
unknown. It was formerly believed that each follicle was 
a kind of secreting-ceU, which, when its contents were 
fully matured, formed a ^^-^ ^g * 

communication with the 
cavity of the intestine by 
the absorption or bursting 
of its own cell-wall, and 
of the portion of mucous 
membrane over it, and 
thus discharged its secre- 
tion into the intestinal 
canal. A small shallow 
cavity or space vvas thought 
to remain, for a time, after 
this absorption or dehi- 
scence, but shortly to disappear, together with all trace of 
the previous gland. 

More recent acquaintance with the real structure of 
these bodies seems, however, to prove that they are not 
mere temporary gland-cells which thus discharge their 
elaborated contents into the intestine and then disappear, 
but that they are rather to be regarded as structures 

* Fig. 78. Side-view of a portion of intestinal mucous membrane of 
a cat, showing a Peyer's gland (a) : it is imbedded in the submucous 
tissue (/), the line of separation between which and the mucous mem- 
brane passes across the gland : h, one of the tubular follicles, the orifices 
of which form the zone of openings around the gland : c, the fossa in 
the mucous membrane : d, villi : e, follicles of Lieberkiihn (after Bendz). 




304 DIGESTION. 

analogous to lymphatic or absorbent glands, and that 
their office is to take up certain materials from the chyle, 
elaborate and subsequently discharge them into the lacteals, 
with which vessels they appear to be closely connected, 
although no direct communication has been proved to 
exist between them. 

Moreover, it has been lately suggested that since the 
molecular and cellular contents of the glands are so 
abundantly traversed by minute blood-vessels, important 

Fig. 79.* 




changes may mutually take place between these contents 
and the blood in the vessels, material being abstracted 
from the latter, elaborated by the cells, and then restored 



* Fig. 79. Transverse section of injected Peyer's glands (from Kol- 
liker). The drawing was taken from a preparation made by Frey : it 
represents the fine capillary looped network spreading from the sm-- 
rounding blood-vessels into the interior of three of Peyer's capsules 
from the intestine of the rabbit. 



BRUNN'S GLANDS. 



305 



to the blood, much, in the same manner as is believed to be 
the case in the so-called vascular glands, such as the spleen, 
thymus, and others ; and that thus Peyer's glands should 
also be regarded as closely analogous to these vascular 
glands. Possibly they may combine the functions both of 
lymphatic and vascular glands, absorbing and elaborating 
material both from the chyle and from the blood within 
their minute vessels, and transmitting part of the lacteal 
system and part direct to the blood. 

Firj. 80.* 




ft 



Brwui's glands (fig. 80) are confined to the duodenum ; f 
they are most abundant and thickly set at the commence- ; 
ment of this portion of the intestine, diminishing gradually 
as the duodenum advances. Situated beneath the mucous 
membrane, and imbedded in the submucous tissue, they 
are minutely lobulated bodies, visible to the naked eye, 
like detached small portions of pancreas, and provided with I 
permanent gland-ducts, which pass through the mucous 
membrane and open on the internal surface of the intestine. 

* Fig. 80. Enlarged view of one of Brunn's glands from the liuman 
duodenum (from Frey). The main duct is seen superiorly ; its branches 
are elsewhere hidden by the bunches of opaque glandular vesicles. 



3o6 DIGESTION. 

As in structure, so probably in function, they resemble the 
pancreas ; or at least stand to it in a similar relation to 
that which the small labial and buccal glands occupy in 
relation to the larger salivary glands, the parotid and 
submaxillary. 

The Villi (figs. 8 1, 82) are confined exclusively to the 
mucous membrane of the small intestine. They are minute 
vascular processes, from a quarter of a line to a line and 
two -thirds in length, covering the surface of the mucous 
membrane, and giving it a peculiar velvety, fleecy appear- 
ance. Krauss estimates them at fifty to ninety in number 
in a square line, at the upper part of the small intestine,. 
and at forty to seventy in the same area at the lower part. 
They vary in form even in the same animal, and differ 
according as the lymphatic vessels they contain are empty 
or full of chyle; being usually, in the former « case, flat 
and pointed at their summits, in the latter cylindrical or 
clavate. 

Each villus consists of a small projection of mucous- 
membrane, and its interior is therefore supported through- 
out by fine retiform or adenoid tissue, which forms thet 
framework or stroma in which the other constituents are 
contained. 

The surface of the villus is clothed by columnar epithe- 
lium, which rests on a fine basement membrane ; while 
within this are found, reckoning from without inwards^ 
blood-vessels, fibres of the muscularis miicosce, and a single 
lymphatic, or lacteal vessel rarely looped or branched (fig. 
81) ; besides granular matter, fat-globules, etc. 

The epithelium is of the columnar kind, and continuous 
with that lining the other parts of the mucous membrane. 
The cells are arranged with their long axis radiating from 
the surface of the villus (fig. 81), and their smaller ends 
resting on the basement membrane. Some doubt exists 
concerning the minute structure of these cells and their 
relation to the deeper parts of the villus. 



THE VILLI. 



307 



Beneath the basement or limiting membrane there is a 
rich supply of blood-vessels. Two or more minute arteries 
are distributed within each villus ; and from their capil- 

Flg. 81.* 




laries, which form a dense network, proceed one or two 
small veins, which pass out at the base of the villus. 

The layer of the muscularis mucosce in the villus forms a 
kind of thin hollow cone immediately around the central 
lacteal, and is, therefore, situate beneath the blood-vessels. 
The addition of acetic acid to the villus brings out the 
characteristic nuclei of the muscular fibres, and shows the 
size and position of the layer most distinctly. Its use is 

* Fig. 81. (Slightly altered from Teichmann.) A. Vilhis of sheep. 
B, Villi of man. 

X 2 



308 DIGESTION. 

still unknown, although it is impossible to resist the belief, 
that it is instrumental in the propulsion of chyle along the 
lacteal. 

Fig. 82.* 




The lacteal vessel enters the base of each villus, and pass- 

* Fig. 82, (From Teichmann. ) A, lacteals in villi. P, Peyer's glands. 
B and D, superficial and deep network of lacteals in submucous tissue. 
L, Lieberkiilin's glands. E, small branch of lacteal vessel on its way to 
mesenteric gland, h and 0, muscular fibres of intestine, s, peritoneum. 



THE LARGE INTESTINE. 



309 



ing up in the middle of it, extends nearly to the tip, where 
it ends commonly by a closed and somewhat dilated ex- 
tremity. In the larger villi there may be two small lacteal 
vessels which end by a loop (fig. 81), or the lacteals may 
form a kind of network in the villus. The last method 
of ending, however, is rarely or never seen in the human 
subject, although common in some of the lower animals 
(a, fig. 81). 

The ofiice of the villi is the absorption of chyle from the 
completely digested food in the intestine. The mode in 
which they effect this will be considered in the chapter on 
Absorption. 

Structure of the Large Intestine. 

The large intestine, which in an adult is from about 4 to 
6 feet long, is subdivided for descriptive purposes into three 
portions, viz. : — The cceciun, a short wide pouch, commu- 
nicating with the lower end of the small intestine through 
an opening, guarded by the ileo-ccecal valve; the colon, 
continuous with the caecum, which forms the principal 
part of the large intestine, and is divided into an ascend- 
ing, transverse and descending portion ; and the rectum^ 
which, after dilating at its lower part, again contracts, 
and immediately afterwards opens externally through the 
anus. Attached to the caecum is the small appendix 
vermifowiis. 

Like the small intestine, the large is constructed of three 
principal coats, viz., the serous, muscular, and mucous. 
The serous coat need not be here particularly described. 
Connected with it are the small processes of peritoneum 
containing fat, called appendices epiploicce. The fibres of 
the muscular coat, like those of the small intestine, are 
arranged in two layers — the outer longitudinally, the 
inner circularly. In the caecum and colon, the longi- 
tudinal fibres, besides being, as in the small intestine, 
thinly disposed in all parts of the wall of the bowel, are 



310 DIGESTION. 

collected, for the most part, into tliree strong bands, wliich 
being shorter, from end to end, than the other coats of 
the intestine, hold the canal in folds, bounding inter- 
mediate sacculi. On the division of these bands, the intes- 
tine can be drawn out to its full length, and it then 
assumes, of course, an uniformly cylindrical form. In the 
rectum, the fasciculi of these longitudinal bands spread 
out and mingle with the other longitudinal fibres, forming 
with them a thicker layer of fibres than exists on any 
other part of the intestinal canal. The circular muscular 
fibres are spread over the whole surface of the bowel, but 
are somewhat more marked in the intervals between the 
sacculi. Towards the lower end of the rectum they become 
more numerous, and at the anus they form a strong band 
called the internal sphincter muscle. 

The mucous membrane of the large, like that of the 
small intestine, is lined throughout by columnar epithe- 
lium, but, unlike it, is quite smooth and destitute of villi, 
and is not projected iDTthe form of valvulsD conniventes. 
Its general microscopic structure resembles that of the 
small intestine. 

Glands of the Large Intestine. — The glands with which 
the large intestine is provided are of two kinds, the tubular 
and lenticular. 

The tubular glands, or glands of Lieberkiihn, resemble 
those of the small intestine, but are somewhat larger 
and more numerous. They are also more uniformly 
distributed. 

The lenticular glands are most numerous in the ca3cum 
and vermiform appendix. They resemble in shape and 
structure, almost exactly, the solitary glands of the small 
intestine, and, like them, have no opening. Just over 
them, however, there is commonly a small depression in 
the mucous membrane, which has led to the erroneous 
belief that some of them open on the surface. 

The functions discharged by the glands found in the 



THE ILEO-C^CAL VALVE. 311 

large intestine are not known with any certainty, but 
there is no reason to doubt that they resemble very nearly 
those discharged by the glands of like structure in the 
small intestine. 

The difficulty of determining the function of any single 
set of the intestinal glands seems indeed almost insuper- 
able, so many fluids being discharged together into the 
intestine ; for all acting, probably, at once, produce a com- 
bined efiect upon the food, so that it is almost impossible 
to discern the share of any one of them in digestion. 

Ileo-ccecal valve. — The ileo-csecal valve is situate at the 
place of junction of the small with the large intestine, and 
guards against any reflux of the contents of the latter into 
the ileum. It is composed of two semilunar folds of mucous 
membrane. Each fold is formed by a doubling inwards of 
the mucous membrane, and is strengthened on the outside 
by some of the circular muscular fibres of the intestine, 
which are contained between the outer surfaces of the two 
layers of which each fold is composed. The inner surface 
of the folds is smooth ; the mucous membrane of the ileum 
being continiious with that of the caecum. That surface 
of each fold which looks towards the small intestine is 
covered with villi, while that which looks to the caecum 
has none. When the caecum is distended, the margins of 
the folds are stretched, and thus are brought into firm 
apposition one with the other. 

While the circular muscular fibres of the bowel at the 
junction of the ileum with the caecum are contained 
between the outer opposed surfaces of the folds of mucous 
membrane which form the valve, the longitudinal mus- 
cular fibres and the peritoneum of the smaU and large 
intestine respectively are continuous with each other, 
without dipping in to follow the circular fibres and the 
mucous membrane. In this manner, therefore, the folding 
inwards of these two last-named structures is preserved, 
while on the other hand, by dividing the longitudinal 



312 DIGESTION.] 

muscular fibres and the peritoneum, the valve can be made 
to disappear, just as the constrictions between the sacculi 
of the large intestine can be made to disappear by perform- 
ing a similar operation. 

The Pancreas, and its Secretion. 

The pancreas is situated within the curve formed by the 
duodenum ; and its main duct opens into that part of the 
intestine, either through a small opening or through a duct 
common to itself and to the liver. The pancreas, in its 
minute anatomy, closely resembles the salivary glands ; 
and the fluid elaborated by it appears almost identical with 
saliva. When obtained pure, in all the different animals 
in which it has been hitherto examined, it has been found 
colourless, transparent, and slightly viscid. It is alkaline 
when fresh, and contains a peculiar animal matter named 
pancreatin, and certain salts, both of which are very similar 
to those found in saliva. In pancreatic secretion, however, 
there is no sulpho-cyanogen. Pancreatin is a substance 
coagulable by heat, and in many other respects very 
like albumen : to it the peculiar digestive power of the 
pancreatic secretion is probably due. Like saliva, the 
pancreatic fluid, shortly after its escape, becomes neutral 
and then acid. 

The following is the mean of three analyses by 
Schmidt : — 

Composition of Pancreatic Secretion. 

Water 980*45 

Sohds 19-55 

Pancreatin 1271 

Inorganic bases and salts . . . . 6 '84 

19-55 

The functions of the pancreas are probably as follows : — 
I. Numerous experiments have shown, that starch is 



THE PANCREATIC SECRETION. 313 

acted upon by the pancreatic secretion, or by portions of 
pancreas put in starch paste, in the same manner that it 
is by saliva and portions of the salivary glands. And 
although, as before stated (p. 262), many substances be- 
sides those glands can excite the transformation of starch 
into dextrin and grape-sugar, yet it appears probable 
that the pancreatic fluid, exercising this power of trans- 
formation, is largely subservient to the purpose of digesting 
starch. MM. Bouchardat and Sandras have shown that 
the raw starch-granules which have passed unchanged 
through the crops and gizzards of granivorous birds, or 
through the stomachs of herbivorous Mammalia, are, in 
the small intestine, disorganized, eroded, and finally dis- 
solved, as they are when exposed, in experiment, to the 
action of the pancreatic fluid. The bile cannot effect such 
a change in starch ; and it is most probable that the pan- 
creatic secretion is the principal agent in the transforma- 
tion, though it is by no means clear that the oflice may 
not be shared by the secretion of the intestinal mucous 
membrane, which also seems to possess the power of con- 
verting starch Into sugar. 

2. The existence of a pancreas in Carnivora, which have 
little or no starch in their food, and the results of various 
observations and experiments, leave very Itttle doubt that 
the pancreatic secretion also assists largely in the digestion 
of fatty matters, by transforming them into a kind of 
emulsion, and thus rendering them capable of absorption 
by the lacteals. Several cases have been recorded in which 
the pancreatic duct being obstructed, so that the secretion 
could not be discharged, fatty or oily matter was abun- 
dantly discharged from the intestines. In nearly aU these 
cases, indeed, the liver was coincidently diseased, and the 
change or absence of the bile might appear to contribute 
to the result ; yet the frequency of extensive disease of 
the liver, unaccompanied by fatty discharges from the 
intestines, favours the view that, in these cases, it is to the 
absence of the pancreatic fluid from the intestines that the 



3 14 DIGESTIOX. 

excretion or non-absorption of fatty matter should be 
ascribed. In Bernard's experiments too, fat always ap- 
peared in the evacuations when the pancreas was destroyed 
or its duct tied. Bernard, indeed, is of opinion that to 
emulsify fat is the express office of the pancreas, and the 
evidence that he and others have brought forward in sup- 
port of this view is very weighty. The power of emulsify- 
ing fat, however, although perhaps mainly exercised by 
the secretion of the pancreas, is evidently possessed to 
some extent by other secretions poured into the intestines, 
and especially by the bile. 

3. The pancreatic secretion discharges a third function 
also, namely, that of dissolving albuminous substances; 
the peptone produced by the action of the pancreatic secre- 
tion on proteids not differing essentially from that formed 
hy the action of the gastric juice (see p. 285). 

Structure of the Liver. 

The liver is an extremely vascular organ, and receives 
its supply of blood from two distinct vessels, the portal 
-vein and hepatic artery, while the blood is returned from it 
into the vena cava inferior by the hepatic vein. Its secre- 
tion, the hile, is conveyed from it by the hepatic duct, either 
■directly into the intestine, or, when digestion is not going 
on, into the cystic duct, and thence into the gall-bladder, 
where it accumulates until required. The portal vein, 
hepatic artery, and hepatic duct branch together throughout 
the liver, while the hepatic vein and its tributaries run by 
themselves. 

On the outside the liver has an incomplete covering of 
peritoneum, and beneath this is a very fine coat of areolar 
tissue, continuous over the whole surface of the organ. 
It is thickest where the peritoneum is absent, and is con- 
tinuous on the general surface of the liver with the fine, 
and, in the human subject, almost imperceptible, areolar 
tissue investing the lobules. At the transverse fissure it is 



STRUCTURE OF THE LIVER. 



315 



merged in the areolar investment called Glisson's capsule. 
Flu Sz^ 

L2 






which, surrounding the portal vein, hepatic artery, and 

hepatic duct, as they enter at 

this part, accompanies them ^'3- ^4- 

in their branchings through 

the substance of the liver. 

The liver is made up of 
small roundish or oval por- 
tions called lobules, each of 
which is about -5-^ of an inch 
in diameter, and composed of 

the minutest branches of the portal vein, hepatic artery, 
hepatic duct, and hepatic vein ; while the interstices of 

* Fig. 83. The liver has been turned over from left to right so as 
to expose the lower surface, i, left lobe ; 2, 3, 4, 5, right lobe ; 
6, lobulus quadratus; 7, jions hepatis; 8, 9, 10, lobulus Spigelii ; 
II, lobulus caudatus ; 12, 13, transverse or portal fissure with the 
great vessels ; 14, hepatic artery ; 15, vena portse ; 16, anterior part 
of the longitudinal fissure, containing 17, the round ligament or ob- 
literated remains of the umbilical vein ; 18, posterior part of the same 
fissure, containing 19, the obliterated ductus venosus ; 20, 21, 22, 
gall-bladder; 23, cystic duct; 24, hepatic duct; 25, fossa containing 



3i6 



DIGESTIOX. 



d a 



these vessels are filled by the liver cells. These cells 
(fig. 84) which make up a great portion of the substance 
of the organ, are rounded or polygonal from about -g-^-^ to 
-j\-^^ of an inch in diameter, containing well-marked nuclei 
and granules, and having sometimes a yellowish tinge, 
especially about their nuclei ; frequently, they contain also 
various sized particles of fat (fig. 84 b). Each lobule is 
vary sparingly invested by areolar tissue. 

Ficj. 85.* To understand the 

distribution of the 
blood-vessels in the 
liver, it will be well 
to trace, first, the two 
blood-vessels and the 
duct which enter the 
organ on the under 
surface at the trans- 
verse fissure, viz., the 
portal vein, hepatic 
arter}^, and hepatic 
duct. As before re- 
marked, all three 
run in company, and 
their appearance on 
longitudinal section 
is shown in fig 85 . Running together through the substance 
of the liver, they are contained in small channels, called 
•portal canals, their immediate investment being a sheath 
of areolar tissue, called Glisson*s capsule. 

26, the vena cava inferior ; 27, opening of the capsular vein ; 28, small 
part of the tmnk of the right hepatic vein ; 29, trunk of the left 
hepatic vein ; 30, 31, openings of the right andleftdiaj)hragmatic veins. 
* Fig. 85. Longitudinal section of a portal canal, containing a portal 
vein, hepatic artery and hepatic duct, from the pig (after Kiernan) f . r, 
branch of vena portte, situated in a portal canal, formed amongst the 
lobules of the liver, and giving off vaginal branches ; there are also 
seen within the large portal vein numerous orifices of the smallest inter- 
lobular veins arising directly from it ; a, hepatic artery ; d, hepatic duct. 




STRUCTURE OF THE LIVER. 



317 



To take the distribution of the portal vein first : — In 
its course through the liver this vessel gives off small 
branches, which divide and subdivide between the lobules 
surrounding them and limiting them, and from this cir- 
cumstance called intei'-lohular veins. From these small 
vessels a dense capillary network is prolonged into the 
substance of the lobule, and this network gradually gather- 
ing itself up, so to speak, into larger vessels, converges 
finally to a single small vein, occupying the centre of the 
lobule, and hence called intr a ■lohnla.r. This arrangement 
is well seen in fig. 86, which represents a transverse sec- 
tion of a lobule. The smaller branches of the portal vein 
being closely surrounded by the lobules, give off directly 

Fir/. 86.* 




inter-lohulsLT veins (see fig. 85) ; but here and there, espe- 
cially where the hepatic artery and duct intervene, branches 

* Fig. 86. Cross section of a lobule of the human liver, in which 
the capillary network between the portal and hepatic veins has been fully 
injected (from Sappey) ^. i. Section of the ^?i^?'a- lobular vein ; 2, its 
smaller branches collecting blood from the capillary network ; 3, inter- 
lobular branches of the vena portse with their smaller ramifications 
jiassing inwards towards the capillary network in the substance of the 
lobule. 



318 



DIGESTIOX. 



called vaginal first arise, and breaking up in the sheath are 
subsequently distributed like the others around the lobules 
and become mter-lohular. The larger trunks of the portal 
vein being more separated from the lobules by a thicker 
sheath of Glisson's capsule, give off vaginal branches 
alone, which, however, after breaking up in the sheath, 
are distributed like the others between the lobules, and 
become inter-lohvLlsLT veins. 

The small f«/m -lobular veins discharge their contents into 
veins called snb-lohvlaT (fig. 88), while these again, by their 

Fig. .87.* 




* Fig. 87. Section of a portion of liver passing longitudinally 
through a considerable hepatic vein, from the pig (after Kiernan) {. H, 
hepatic venous trunk, against which the sides of the lobules (J.) are 
applied ; 7i, h, 7i, sul^lobular hepatic veins, on which the bases of the 
lobules rest, and through the coats of which they are seen as polygonal 
figures ; i, mouth of the intralobular veins, opening into the sublobular 
veins ; i', intralobular veins shown passing up the centre of some divided 
lobules ; I, I, cut surface of the liver ; c, c, walls of the hepatic_venous 
canal, fonned by the polygonal bases of the lobules. 



STRUCTUEE OF THE LIVEE. 



319 




union, form the main branches of the hepatic vein, whick 
leaves the posterior border of 
the liver to end by two or Fig. 88.* 

three principal trunks in the /fe^ 

inferior vena cava, just before 
its passage through the dia- 
phragm. The s?^& -lobular and 
hepatic veins, unlike the portal 
vein and its companions, have 
little or no areolar tissue 
around them, and their coats 
being very thin, they form 
little more than mere chan- 
nels in the liver substance 
which closely surrounds them. 

The manner in which the lobules are connected with 
the suhlobular veins by means of the small intralohular vein& 
is well seen in the diagram, fig. ^^ and in fig. ^y, which 
represent the parts as seen in a longitudinal section. The 
appearance has been likened to a twig having leaves with- 
out footstalks — the lobules representing the leaves, and 
the suhlobular vein the small branch from which it springs.. 
On a transverse section, the appearance of the intra- 
lohular veins is that of I, fig. ^6, while both a transverse 
and longitudinal section are exhibited in fig. 89. 

The hepatic artery, the function of which is to distribute 
blood for nutrition to Glisson's capsule, the walls of the 
ducts and blood-vessels, and other parts of the liver, is, 
distributed in a very similar manner to the portal vein, its 
blood being returned by small branches either into the 
ramifications of the portal vein, or into the capillary plexus, 
of the lobules which connects the inter- and intra-lohvloir 
veins. 



* Fig. 88. Diagi-am sliowing the manner in which the lobules of the 
liver rest on the suhlobular veins (after Kiernan). 



320 DIGESTION. 

The hepatic duct divides and subdivides in a manner 
very like that of the portal vein and hepatic artery, the 
larger branches being lined by cylindrical, and the smaller 

F!f/, 89.* 




by small polygonal epithelium. The exact arrangement of 
its terminal branches, however, and their relatoin to the 
liver-cells have not been clearly made out, or, at least, have 
not been agreed upon by different observers. The chief 
theories on the subject are three in number : — 

1. That the terminal branches of the hepatic duct form 
an interlobular network, which abuts on the outermost 
cells of a lobule, but does not enter the inside of the 
lobule, or only for a little way. 

2. That minute branches begin in the lobules between 
the cells, not enclosing them. 

3. That the ultimate branches begin in the lobules and 
enclose hepatic cells. 

* Fig. 89. Capillary network of the lobules of the rabbit's liver 
(from Kolliker), ~. The figure is taken from a very successful injec- 
tion of the hepatic veins, made by Harting : it shoAvs nearly the whole 
of two lobules, and parts of three others ; p, jwrtal branches running in 
the interlobular spaces ; 7i, hepatic veins penetrating and radiating from 
the centre of the lobules. 



STKUCTUEE OF THE LIVER. 



321 



The illustrations below will show the conflicting theories 
at a glance. 

Flrj. 90.* 






* Fig. 90, Diagrams showing the aiTangeiiient of the radicles of the 
hepatic duct, according to different observers. 

1. d, dy are two branches of the hepatic duct, which is sup|)osed 
to commence in a plexus situated towards the circumference of the 
lobule marked b, h, called by Kiernan the biliary plexus. Within this 
is seen the central part of the lobule, containing branches of the intra- 
lobular vein, 

2. A small fragment of an hepatic lobule, of which the smallest 
intercellular biliary ducts were filled with colouring matter during 
^ifo, highly magnified (from Chrzonszczewsky). 

3. View of some of the smallest biliary ducts illustrating Beale's 
view of their relation to the biliary cells (from KoUiker after Beale),-p . 

The drawing is taken from an injected preparation of tlie pig's liver ; 

Y 



;22 DIGESTION. 



Functions of the Liver, 

The Secretion, of Bile is the most obvious, and one of the 
chief functions which the Kver has to perform ; but, as 
will be presently shown, it is not the only one ; for im- 
portant changes are effected in certain constituents of the 
blood in its transit through this gland, whereby they are 
rendered more fit for their subsequent purposes in the 
animal economy. 

The Bile, 

Composition of the Bile. — The bile is a somewhat viscid 
fluid, of a yeUow or greenish-yellow colour, a strongly 
bitter taste, and when fresh with a scarcely perceptible 
odour ; it has a neutral or slightly alkaline reaction, and 
its specific gravity is about I020. Its colour and degree 
of consistence vary much, apparently independent of 
disease ; but, as a rule, it becomes gradually more deeply 
coloured and thicker as it advances along its ducts, or 
when it remains long in the gall-bladder, wherein, at 
the same time, it becomes more viscid and ropy, of a 
darker colour, and more bitter taste, mainly from its 
greater degree of concentration, on account of partial 
absorption of its water, but partly also from being mixed 
with mucus. 

The following analysis is by Frerichs : — 

Composition of Human Bile, 

Water 859*2 

Solids 140-8 



a, small branch of an interlobular hepatic duct ; h, smallest biliary 
ducts ; c, portions of the cellular part of the lobule in which the cells 
are seen within tubes which communicate with the finest ducts. 



THE BILE. 

Biliary acids combined )g.ij^ ^ ^ 

with alkalies j ^ •' 

Fat . 9-2 

Cholesterin . . . . 2 '6 

Mucus and colouring matters . . . 29 "8 

Salts 77 



323 



140-5 



The Bilin or biliary matter when freed by etlier from the 
fat with which it is combined, is a resinoid substance, solu- 
ble in water, alcohol, and alkaline solutions, and giving to 
the watery solution the taste and general character of bile. 
It is a compound of soda, with two resinous acids, named 
glycocholic and taurocholic acids. The^ former consists of 
cholic acid conjugated with glycin (or sugar of gelatin), the 
latter of the same acid conjugated with taurin. 

Fatty substances are found in variable proportions. Be- 
sides the ordinary saponifiable fats, there is a small quantity 
of cholesterin (p. ii), which, with the other free fats, is 
probably held in solution by the tauro-cholate of soda. 

A peculiar substance, which Dr. Flint has discovered in 
the faeces, and named stercorin (p. 342), is closely allied 
to cholesterin ; and Dr. Flint Fig. 91.* 

believes that while one great 
function of the liver is to ex- 
crete cholesterin from the 
blood, as the kidney excretes 
urea, the stercorin of faeces 
is the modified form in which 
cholesterin finally leaves the 
body. Ten grains and a half 
of stercorin, he reckons, are 
excreted daily. 

The colouring matter of the bile has not yet been obtained 
pure, owing to the facility with which it is decomposed. 
It occasionally deposits itself in the gall-bladder as a 

* Fig. 91. Crystalline scales of cholesterin, 

y 2 




324 DIGESTION. 

yellow substance mixed with mucus, and in this state has 
been frequently examined. It is composed of two coloiir- 
ing matters, called hiliverdin and bilifulvm. By oxidising 
agencies, as exposure to the air, or the addition of nitric 
acid, it assumes a dark green colour. In cases of biliary 
obstruction, it is often re-absorbed, circulates with the blood, 
and gives to the tissues the yeUow tint characteristic of 
jaundice. 

There seems to be some relationship between the colour- 
matters of the blood and bile, and, it may be added, be- 
tween these and that of the urine also, so that it is possible 
they may be, all of them, varieties of the same pigment, 
or derived from the same source. Nothing, however, is at 
present certainly known regarding the relation in which 
one of them stands to the other. 

The mucus in bile is derived chiefly from the mucous 
membrane of the gall-bladder, but in part also from the 
hepatic ducts and their branches. It constitutes the residue 
after bile is treated with alcohol. The epithelium with 
which it is mixed may be detected in the bile with the 
microscope in the form of cylindrical cells, either scattered 
or still held together in layers. To the presence of this 
mucus is probably to be ascribed the rapid decomposition 
undergone by the bilin ; for, according to Berzelius, if the 
mucus be separated, bile will remain unchanged for many 
days. 

The saline or inorganic constituents of the bile are similar 
to those found in most other secreted fluids. It is possible 
that the carbonate and neutral phosphate of sodium and 
potassium, found in the ashes of bile, are formed in the 
incineration, and do not exist as such in the fluid. Oxide 
of iron is said to be a common constituent of the ashes of 
bile, and copper is generally found in healthy bile, and 
constantly in biliary calculi. 

Such are the principal chemical constituents of bile ; but 



THE BILE. 



325 



I 



its physiology is, perhaps, better illustrated by its ultimate 
elementary composition. According to Liebig's analysis, 
the biliary matter, — consisting of bilin and the products of 
its spontaneous decomposition — yields, on analysis, 76 atoms 
of carbon, 66 of hydrogen, 22 of oxygen, 2 of nitrogen, 
and a certain quantity of sulphur.* Comparing this with 
the ultimate composition of the organic parts of blood, 
which may be stated at C^gH^gNgOj^ with sulphur and 
phosphorus — it is evident that bile contains a large pre- 
ponderance of carbon and hydrogen, and a deficiency of 
nitrogen. The import of this will presently appear. 

Tests fok Bile. — A common test for the presence of 
bile consists of the addition of a small quantity of nitric 
acid, when, if bile be present, a play of colours is produced, 
beginning with green and passing through various tints 
to red. This test will detect only the colouring matter of ' 
the bile. 

The best test for the bilin is Pettenkofer's. To the liquid/* 
suspected to contain bile must be added, first, a drop or twq 
of a strong solution of cane-sugar (one part of sugar to 
four parts of water), and immediately afterwards sulphuric , 
acid, to the extent of about two -thirds of the liquid. On 
first adding the acid, a whitish precipitate falls ; but this 
redissolves with a slight excess of the acid, and on the 
further addition of the latter there appears a bright cherry- 
red colour, gradually changing through a lake tint, to a dark 
purple. 

The process of secreting bile is probably continually going 
on, but appears to be retarded during fasting, and accele- 
rated on taking food. This was shown by Blondlot, who, 



* The sulphur is combined with the taurin — one of the substances 
yielded by the decomposition of bilin. According to Dr. Kemp, the 
sulphur in the bile of the ox, dried and freed from mucus, colouring 
matter, and salts, constitutes about 3 per cent. 



326 DIGESTION. 

having tied the common bile-duct of a dog, and established 
a fistulous opening between the skin and gall-bladder, 
whereby aU the bile secreted was discharged at the surface, 
noticed that when the animal was fasting, sometimes not 
a drop of bile was discharged for several hours ; but 
that, in about ten minutes after the introduction of food 
into the stomach, the bile began to flow abundantly, and 
continued to do so during the whole period of digestion. 
Bidder and Schmidt's observations are quite in accordance 
with this. 

The bile is probably formed first in the hepatic cells ; 
then, being discharged into the minute hepatic ducts, it 
passes into the larger trunks, and from the main hepatic 
duct may be carried at once into the duodenum. But, 
probably, this happens only while digestion is going on ; 
during fasting it flows from the common bile-duct into 
the cystic duct, and thence into the gall-bladder, where it 
accumulates till, in the next period of digestion, it is dis- 
charged into the intestine. The gall-bladder thus fulfils 
w^hat appears to be its chief or only office, that of a reser- 
voir ; for its presence enables bile to be constantly secreted 
for the purification of the blood, j^et insures that it shall all 
be employed in the service of digestion, although digestion 
is periodic, and the secretion of bile constant. 

The mechanism by which the bile passes into the gall- 
bladder is simple. The orifice through which the common 
bile-duct communicates with the duodenum is narrower 
than the duct, and appears to be closed, except when there 
is sufficient pressure behind to force the bile through it. 
The pressure exercised upon the bile secreted during the 
intervals of digestion appears insufficient to overcome the 
force with which the orifice of the duct is closed ; and the 
bile in the common duct, finding no exit in the intestine, 
traverses the cystic duct, and so passes into the gaU-bladder, 
being probably aided in this retrograde course by the peri- 
staltic action of the ducts. The bile is discharged from the 



THE BILE: MECONIUM. 327 

gaU-bladder, and enters the duodenum on the introduction 
of food into the small intestine : being pressed on by the 
contraction of the coats of the gall-bladder, and probably 
of the common bile-duct also ; for both these organs contain 
organic muscular fibre -ceUs. Their contraction is excited 
by the stimulus of the food in the duodenum acting so as to 
produce a reflex movement, the force of which is sufficient 
to open the orifice of the common bile-duct. 

Various estimates have been made of the quantity of bile 
discharged in the intestines in twenty-four hours: the 
quantity doubtless varjdng, like that of the gastric fluid, in 
proportion to the amount of food taken. A fair average 
of several computations would give thirty to forty ounces 
as the quantity daily secreted by man. 

The purposes served by the secretion of bile may be con- 
sidered to be of two principal kinds, viz., excrementitious 
and digestive. 

As an excrementitious substance, the bile serves especi- 
ally as a medium for the separation of excess of carbon and 
hydrogen from the blood ; and its adaptation to this pur- 
pose is well illustrated by the peculiarities attending its 
secretion and disposal in the foetus. During intra-uterine 
life, the lungs and the intestinal canal are almost inactive; 
there is no respiration of open air or digestion of food ; 
these are unnecessary, because of the supply of weU-elabo- 
-rated nutriment received by the vessels of the foetus at the 
placenta. The liver, during the same time, is proportionally 
larger than it is after birth, and the secretion of bile is 
active, although there is no food in the intestinal canal upon 
which it can exercise any digestive property. At birth, the 
intestinal canal is full of thick bile, mixed with intestinal 
•secretion; for the meconium, or feeces of the foetus, are 
shown by the analyses of Simon and of Frerichs to contain 
aU the essential principles of bile. 



328 DIGESTION. 

Composition of Meconium (Frerichs) : 

Biliary resin 15-6 

Common fat and cholesterin 15*4 

Epithelium, mucus, pigment, and salts . . 69 * 



In the foetus, therefore, the main purpose of the secretion 
of bile must be the purification of the blood by direct 
excretion, i.e., by separation from the blood, and ejection 
from the body without further change. Probably all the 
bile secreted in foetal life is incorporated in the meconium, 
and with it discharged, and thus the liver may be said to 
discharge a function in some sense vicarious of that of the 
lungs. For, in the foetus, nearly all the blood coming from 
the placenta passes through the liver, previous to its dis- 
tribution to the several organs of the body; and the 
abstraction of carbon, hydrogen, and other elements of bile 
will purify it, as in extra-uterine life it is purified by the 
separation of carbonic acid and water at the lungs. 

The evident disposal of the foetal bile by excretion, makes 
it highly probable that the bile in extra-uterine life is 
also, at least in part, destined to be discharged as 
excrementitious. But the analysis of the feeces of both 
children and adults shows that (except when rapidly dis- 
charged in purgation) they contain very little of the bile 
secreted, probably not more than one-sixteenth part of its 
weight, and that this portion includes only its colouring, 
and some of its fatty matters, but none of its essential 
principle, the bilin. All the bilin is again absorbed from 
the intestines into the blood. But the elementary compo- 
sition of bilin (see p. 325) shows such a preponderance of 
carbon and hydrogen, that it cannot be appropriated to 
the nutrition of the tissues ; therefore, it may be presumed 
that after absorption, the carbon and hydrogen of the 
bilin combining with oxygen, are excreted as carbonic 
acid and water. The destination of the bile is, on this 



THE BILE. 329 

theory, essentially the same in both foetal and extra- 
uterine life ; only, in the former, it is directly excreted, in 
the latter for the most part indirectly, being, before final 
ejection, modified in its absorption from the intestines, and 
mingled with the blood. 

The change from the direct to the indirect mode of 
excretion of the bile may, with much probability, be con- 
nected with a purpose in relation to the development of 
heat. The temperature of the foetus is maintained by that 
of the parent, and needs no soiurce of heat within the 
body of the foetus itself; but, in extra-uterine life, there is 
(as one may say) a waste of material for heat when any 
excretion is discharged unoxidized ; the carbon and hydro- 
gen of the biKn, therefore, instead of being ejected in the 
faeces, are re-absorbed, in order that they may be combined 
with oxygen, and that, in the combination, heat may be 
generated. 

From the peculiar manner in which the liver is supplied 
with much of the blood that flows through it, it is probable, 
as Dr. Budd suggests, that this organ is excretory, not 
only for such hydro-carbonaceous matters as may need 
expulsion from any portion of the blood, but that it serves 
for the direct purification of the stream which, arriving by 
the portal vein, has just gathered up various substances 
in its course through the digestive organs — substances 
which may need to be expelled, almost immediately after 
their absorption. For it is easily conceivable that many 
things may be taken up during digestion, which not only 
are unfit for pui'poses of nutrition, but which would be 
positively injurious if allowed to mingle with the general 
mass of the blood. The liver, therefore, may be supposed 
placed in the only road by which such matters can pass 
into the general current, jealously to guard against their 
further progress, and turn them back again into an 
excretory channel. The frequency with which metallic 
poisons are either excreted by the liver or intercepted and 



330 DIGESTION. 

retained, often for a considerable time, in its own substance, 
may be adduced as evidence for the probable truth of this 
supposition. 

Though one chief purpose of the secretion of bile may 
thus appear to be the purification of the blood by ultimate 
excretion, yet there are many reasons for believing that, 
while it is in the intestines, it performs an important part in 
the process of digestion. In nearly all animals, for example, 
the bile is discharged, not through an excretory duct 
communicating with the external surface or with a simple 
reservoir, as most secretions are, but is made to pass into 
the intestinal canal, so as to be mingled with the chyme 
directly after it leaves the stomach ; an arrangement, the 
constancy of which clearly indicates that the bile has some 
important relations to the food with which it is thus mixed. 
A similar indication is furnished also by the fact that the 
secretion of bile is most active, and the quantity discharged 
into the intestines much greater, during digestion than at 
any other time ; although, without doubt, this activity of 
secretion during digestion may, however, be in part 
ascribed to the fact that a greater quantity of blood is sent 
through the portal vein to the liver at this time, and that 
this blood contains some of the materials of the food 
absorbed from the stomach and intestines, which may need 
to be excreted, either temporarily, to be re-absorbed, or 
permanently. 

Respecting the functions discharged by the bile in 
digestion, there is little doubt that it assists in emulsifying 
the fatty portions of the food, and thus rendering them 
capable of being absorbed by the lacteals. For it has 
appeared in some experiments in which the common bile- 
duct was tied, that although the process of digestion in the 
stomach was unaffected, chyle was no longer well-formed ; 
the contents of the lacteals consisting of clear, colourless 
fluid, instead of being opaque and white, as they ordinarily 
are, after feeding. (2.) It is probable, also, from the 



FUXCTIOXS OF THE LIYEE. 331 

result of some experiments by Wistinghausen and Hoff- 
mann, that the moistening of the mucous membrane of the 
intestines by bile may facilitate absorption of fatty matters 
through it. 

(3.) The bile, like the gastric fluid, has a strongly 
antiseptic power, and may serve to prevent the decompo- 
sition of food during the time of its sojourn in the intes- 
tines. The experiments of Tiedemann and Gmelin show 
that the contents of the intestines are much more foetid 
after the common bile-duct has been tied than at other 
times ; and the experiments of Bidder and Schmidt on 
animals with an artificial biliary fistula, confirm this 
observation ; moreover, it is found that the mixture of bile 
with a fermenting fluid stops or spoils the process of fer- 
mentation. 

(4.) The bile has also been considered to act as a kind 
of natural purgative, by promoting an increased secretion 
of the intestinal glands, and by stimulating the intestines 
to the propulsion of their contents. This view receives 
support from the constipation which ordinarily exists in 
jaundice, from the diarrhoea which accompanies excessive 
secretion of bile, and from the purgative properties of 
ox-gall. 

Nothing is known with certainty respecting the changes 
which the re-absorbed portions of the bile undergo, either 
in the intestines or in the absorbent vessels. That they 
are much changed appears from the impossibility of 
detecting them in the blood ; and that part of this change 
is effected in the liver is probable from an experiment 
•of Magendie, who found that when he injected bile 
into the portal vein a dog was unharmed, but was 
killed when he injected the bile into one of the systemic 



The secretion of bile, as already observed, is only one 
of the purposes fulfilled by the liver. Another very im- 
portant function appears to be that of so acting upon 



332 DIGESTION. 

certain constituents of the blood passing tlirougli it, as to 
render some of them capable of assimilation with the 
blood generally, and to prepare others for being duly 
eliminated in the process of respiration. From the labours 
of M. Bernard, to whom we owe most of what we know 
on this subject, it appears that the low form of albuminous 
matter, or albuminose, conveyed from the alimentary 
canal by the blood of the portal vein, requires to be sub- 
mitted to the influence of the liver before it can be 
assimilated by the blood ; for if such albuminous matter is 
injected into the jugular vein, it speedily appears in the 
urine; but if introduced into the portal vein, and thus 
allowed to traverse the liver, it is no longer ejected as a 
foreign substance, but is probably incorporated with the 
albuminous part of the blood. 

An important influence seems also to be exerted by the 
liver upon the saccharine matters derived from the alimen- 
tary canal. The chief purpose of the saccharine and 
amylaceous principles of food is, probably, in relation to 
respiration and the production of animal heat; but in 
order that they may fulfil this, their main ofiice, it seems 
to be essential that they should undergo some intermediate 
change, which is effected in the liver, and which consists 
in their conversion into a peculiar form of saccharine 
matter, very similar to glucose, or diabetic sugar. That 
such influence is exerted by the liver seems proved by the 
fact that when cane sugar is injected into the jugular vein 
it is speedily thrown out of the system, and appears in the 
urine; but when injected into the portal vein, and thus 
enabled to traverse the liver, it ceases to be excreted at the 
kidneys ; and, what is still more to the point, a very large 
quantity of glucose may be injected into the venous system 
without any trace of it appearing in the urine. So that it 
may be concluded, that the saccharine principles of the 
food undergo, in their passage through the liver, some 
transformation necessary to the subsequent purpose they 



FORMATION OF SUGAR IN THE LIVER. 333 

have to fulfil in relation to the respiratory process, and 
without which, such purpose probably could not be pro- 
perly accomplished, and the substances themselves would 
be eliminated as foreign matters by the kidneys. 

Then, again, it was discovered by Bernard, and the 
discovery has been amply confirmed, that the liver pos- 
sesses the remarkable property of forming glucose or grape- 
sugar (CgHj20g), or a substance readily convertible into 
sugar, even out of principles in the blood which contain no 
trace of saccharine or amylaceous matter. In Herbivora 
and in animals living on mixed diet, a large part of the 
sugar is derived from the saccharine and amylaceous 
principles introduced in their food. But in animals fed 
exclusively on flesh, and deprived therefore of this source 
of sugar, the liver furnishes the means whereby it may be 
obtained. Not only in Carnivora, however, but apparently 
in all classes of animals, the liver is continually engaged, 
during health, in forming sugar, or a substance closely 
allied to it, in large amount. This substance may always 
be found in the liver, even when absent from all other parts 
of the body. 

To demonstrate the presence of sugar in the liver, a por- 
tion of this organ, after being cut into small pieces, is j 
bruised in a mortar to a pulp with a smaU quantity of J 
water, and the pulp is boiled with sulphate of soda in order ^ 
to precipitate albuminous and colouring matters. The de- \ 
coction is then filtered and. may be tested for glucose. The 
most usual test is Trommer's. To the filtered solution an 
equal quantity of liquor potassao is added, with a few drops | 
of a solution of sulphate of copper. The mixture is then \ 
boiled, when the presence of sugar is indicated by a reddish- j 
brown precipitate of the suboxide of copper. 

The researches of Bernard and others, however, have 
shown that the sugar is not formed at once at the liver, 
but that this organ has the power of producing a peculiar 
substance allied to starch, which is readily convertible into 



334 DIGESTION. 

glucose when in contact with any animal ferment. This 
substance has received the different names of glycogen, 
glycogenic substance, animal starch, hepatin. 

Glycogen (C , ^H j ^O j q) is obtained by taking a portion 
of liver from a recently killed animal, and, after cutting it 
into small pieces, placing it for a short time in boiling 
water. It is then bruised in a mortar, until it forms a 
pulpy mass, and subsequently boiled in distilled water for 
about a quarter of an hour. The glycogen is precipitated 
from the filtered decoction by the addition of alcohol. 

When purified, glycogen is a white, amorphous, starch- 
like substance, odourless and tasteless, soluble in water, 
but insoluble in alcohol. It is converted into glucose by 
boiling with dilute acids, or by contact with any animal 
ferment. 

There are two chief theories concerning the immediate 
destination of glycogen, (i.) According to Bernard and 
most other physiologists, its conversion into sugar takes 
place rapidly during life, and the sugar is conveyed away 
by the blood of the hepatic veins to be consumed in 
respiration at the lungs. (2.) Pavy and others believe that 
the conversion into sugar only occurs after death, and that 
during life no sugar exists in healthy livers, — the amyloid 
substance or glycogen being prevented by some force from 
undergoing the transformation. The chief arguments 
advanced by Pavy in support of this view are, first, that 
scarcely a trace of sugar is found in blood drawn during 
life from the right ventricle, or in blood collected from the 
right side of the heart immediately after an animal has 
been suddenly deprived of life, while if the examination be 
delayed for a little while after death, sugar in abundance 
may be found in such blood; secondly, that the liver, 
like the venous blood in the heart, is, at the moment of 
death, almost completely free from sugar, although after- 
wards its tissue speedily becomes saccharine, unless the 
formation of sugar be prevented by freezing, boiling, or 



t 



FORMATION OF SUGAR IN THE LIVER. 335 

other means calculated to interfere with the action of a 
ferment on the amyloid substance of the organ. Instead 
of adopting Bernard's view, that normally, during life, 
glycogen passes as sugar into the hepatic venous blood, and 
thereby is conveyed to the lungs to be further disposed of, 
Pavy inclines to believe that it may represent an interme- 
diate stage in the formation of fat from materials absorbed 
from the alimentary canal. 

For the present we must remain uncertain as to which 
of these theories contains most truth in it. 

Whatever be the destination of this peculiar amyloid 
substance formed at the liver, most recent observers agree 
that it is formed at, and exists within, the hepatic cells, 
from which it may be extracted by the process just de- 
scribed. 

Much doubt exists also respecting the mode in which 
glycogen is formed in the liver, and the materials 
which furnish its source. Since its quantity is increased 
after feeding, especially on substances containing much 
sugar or starch, it is probable that part of it is derived 
from saccharira principles absorbed from the digestive 
canal ; but since its formation continues even when there 
is no starch or sugar in the food, the albuminous or fatty 
principles also have been thought capable of furnish- 
ing part of it. Numerous experiments, however, having 
proved that the liver continues to form sugar in animals 
after prolonged starvation, and during hybernation, and 
even after death, its production is clearly independent 
of the elements of food. One of Bernard's experiments 
may be quoted in proof of this : — Having fed a healthy dog 
for many days exclusively on flesh, he killed it, removed 
the liver at once, and before the contained blood could 
have coagulated, he thoroughly washed out its tissue by 
passing a stream of cold water through the portal vein. 
He continued the injection until the liver was completely 
exsanguined, until the issuing water contained not a trace 



336 DIGESTION. 

of sugar or albumen, and until no sugar was yielded by- 
portions of the organ cut into slices and boiled in water. 
Having thus deprived the liver of all saccharine matter, 
he left it for twenty-four hours, and on then examining it, 
found in its tissue a large quantity of soluble sugar, which 
must clearly have been formed subsequently to the organ 
being washed, and out of some previously insoluble and 
non-saccharine substance. This and other experiments 
led him and others to the conclusion that the formation 
of the amyloid substance by the liver is the result of a 
kind of secretion or elaboration out of materials in the 
solid tissues of the gland — such secretion being probably 
effected by the hepatic cells, in which, indeed, as already 
observed, the substance has been detected. 

According to this view, then, the liver may be regarded 
as an organ engaged in forming two kinds of secretion, 
namely, bile and sugar, or rather, glycogen readily con- 
vertible into sugar. The former, chiefly excrementitious, 
passes along the bile-ducts into the intestines, where it 
may subserve some purposes in relation to digestion, and 
is then for the most part re-absorbed, and idtimately 
eliminated during the processes concerned in the produc- 
tion of animal heat. The latter, namely sugar, being 
soluble, is, unless Pavy's view be correct, taken up by the 
blood in the hepatic vein, conveyed through the right side 
of the heart to the lungs, where it is probably consumed in 
the respiratory process, and thus contributes to the pro- 
duction of animal heat. 

The formation of glycogen or of sugar is, like all other 
processes in the living body, under the control of the 
nervous system. Bernard discovered that by pricking the 
floor of the fourth ventricle, the quantity of sugar formed 
was so much in excess of the normal quantity, as to be ex- 
creted by the kidney, and thus produce the leading symptom 
of diabetes. Section of the inferior cervical ganglion of the 
sympathetic nerve also produces diabetes. 



DIGESTION IN SMALL INTESTINE. 337 

The channel by which, the influence of the nervous 
system is conducted in the preceding and similar experiments 
is not accurately known ; no theory having been perma- 
nently established, which explains all the facts hitherto 
observed in connection with the influence of the nervous 
system on the production of glucose. 

Summary of the Changes which take place in the Food during 
its Passage through the Small Intestine. 

In order to understand the changes in the food which 
occur during its passage through the small intestine, it 
will be well to refer briefly to the state in which it leaves 
the stomach through the pylorus. It has been said 
before, that the chief office of the stomach is not only to 
mix into an uniform mass all the varieties of food that 
Teach it through the oesophagus, but especially to dissolve 
the nitrogenous portion by means of the gastric juice. 
The fatty matters, during their sojourn in the stomach, 
become more thoroughly mingled with the other consti- 
tuents of the f jod taken, but are not yet in a state fit for 
absorption. The conversion of starch into sugar, which 
began in the mouth, has been interfered with, although 
not stopped altogether. The soluble matters — both those 
which were so from the first, as sugar and saline matter, 
and those which have been made so by the action of the 
saliva and gastric juice — have begun to disappear by ab- 
sorption into the blood-vessels, and the same thing has 
befallen such fluids as may have been swallowed, — wine, 
water, etc. 

The thin pultaceous chyme, therefore, which, during the 
whole period of gastric digestion, is being constantly 
squeezed or strained through the pyloric orifice into the 
duodenum, consists of albuminous matter, broken down, 
dissolving and half dissolved, fatty matter, broken down, 
but not dissolved at all, starch very slowly in process of 



338 DIGESTION. 

conversion into sugar, and as it becomes sugar, also dis- 
solving in the fluids with which it is mixed ; while witk 
these are mingled gastric fluid, and fluid that has been, 
swallowed, together with such portions of the food as are 
not digestible, and will be finally expelled as part of the 
faeces. 

On the entrance of the chyme into the duodenum, it is 
subjected to the influence of the fluid secreted by Lieber- 
kiihn's and Brunn's glands, before described, and to that 
of the bile and pancreatic juice, which are poured into this 
part of the intestine. 

Without doubt, that part of digestion which it is a chief 
duty of the small intestine to perform, is the alteration of 
the fat in such a manner as to make it fit for absorption ► 
And there is no doubt that this change is chiefiy effected 
in the upper part of the small intestine. What is the 
exact share of the process, however, allotted respectively 
to the bile, pancreatic secretion, and the secretion of the 
intestinal glands, is still uncertain. It is most probable, 
however, that the pancreatic secretion and the bile are 
the main agents in emulsifying the fat, and that they dO' 
this by direct admixture with it. They also promote its 
absorption by moistening the surface of the viUi (p. 331). 

During digestion in the small intestine, the viUi become 
turgid with blood, their epithelial cells become filled, by 
absorption, with fat-globules, which, after minute division,, 
transude into the granular basis of the villus, and thence 
into the lacteal vessel in the centre, by which they are 
conveyed along the mesentery to the lymphatic glands, 
and thence into the thoracic duct. A part of the fat is 
also absorbed by the blood-vessels of the intestine. The 
term chyle is sometimes applied to the emulsified contents 
of the intestine after their admixture with the bile and 
pancreatic juice ; but more strictly to the fluid contained in 
the lacteal vessels during digestion, which differs from 
ordinary lymph contained in the same vessels at other times,. 



DIGESTION IN SMALL INTESTINE. 339 

chiefly in tlie greatly increased quantity of fat particles 
which, have been absorbed from the small intestine. 

Although the most evident function of the small intes- 
tine is the digestion of fat, it must not be forgotten that 
a great part of the other constituents of the food is by no 
means completely digested when it leaves the stomach. 
Indeed, its leaving it unabsorbed would, alone, be proof of 
this fact. 

The albuminous substances which have been partly dis- 
solved in the stomach continue to be acted on by the 
gastric juice which passes into the duodenum with them, 
and the effect of the last-named secretion is assisted or 
complemented by that of the pancreas and intestinal 
glands. As the albuminous matters are dissolved, they 
are absorbed chiefly by the blood-vessels, and only to a 
small extent, probably, by the lacteals. 

The starchy, or amylaceous portion of the food, the con- 
version of which into dextrin and sugar was more or less 
interrupted during its stay in the stomach, is now acted 
on briskly by the secretion of the pancreas, and of Brunn's 
glands, and porhaps of Lieberkiihn's glands also, and the 
sugar as it is formed dissolves in the intestinal fluids, and 
afterwards, like the albumen, is absorbed chiefly by the 
blood-vessels. 

The liquids, swallowed as such, which may have escaped 
absorption in the stomach, are absorbed probably very 
soon after their entrance into the intestine ; the fluidity of 
the contents of the latter being preserved more by the con- 
stant secretion of fluid by the intestinal glands, pancreas, 
and liver, than by any given portion of fluid, whether 
swallowed or secreted, remaining long unabsorbed. From 
this fact, therefore, it may be gathered that there is a 
kind of circulation constantly proceeding from the intestines 
into the blood, and from the blood into the intestines 
again ; for, as all the fluid, probably a very large amount, 
secreted by the intestinal glands, must come from the 

z 2 



340 DIGESTION. 

blood, tlie latter would be too mucli drained, were it not 
that the same fluid after secretion is again re-absorbed 
into the current of blood — going into the blood charged 
with nutrient products of digestion — coming out again by 
secretion through the glands in a comparatively uncharged 
condition. 

It has been said before that the contents of the stomach 
during gastric digestion have a strongly acid reaction. 
On the entrance of the chyme into the small intestine, 
this is gradually neutralized to a greater or less degree by 
admixture with the bile and other secretions with which 
it is mixed, and the acid reaction becomes less and less 
strongly marked as the chyme passes along the canal 
towards the ileo-csecal valve. 

Thus, all the materials of the food are acted on in the 
small intestine, and a great portion of the nutrient matter 
is absorbed — the fat chiefly by the lacteals, the other 
principles, when in a state of solution, chiefly by the blood- 
vessels, but neither, probably, exclusively by one set of 
vessels. At the lower end of the small intestine, the chyme, 
still thin and pultaceous, is of a light yellow colour, and 
has a distinctly faecal odour. In this state it passes 
through the ileo-csecal opening into the large intestine. 

Summary of the Process of Digestion in the Large Intestine, 

The changes which take place in the chyme after its 
passage from the small into the large intestine are probably 
only the continuation of the same changes that occur in 
the course of the food's passage through the upper part of 
the intestinal canal. From the absence of villi, however, 
we may conclude that absorption, especially of fatty 
matter, is in great part completed in the small intestine, 
while, from the still half-liquid, pultaceous consistence of 
the chyme when it first enters the caecum, there can be no 
doubt that the absorption of liquid is not by any means 



DIGESTION OF LAEGE INTESTINE. 341 

concluded. The peculiar odour, moreover, whicli is 
acquired after a short time by the contents of the large 
bowel, would seem to indicate the addition to them, in 
this region, of some special matter, probably excretory. 
The acid reaction, which had become less and less distinct 
in the small bowel, again becomes very manifest in the 
caecum — probably from acid fermentation processes in some 
of the materials of the food. 

There seems no reason, however, to conclude that any 
special, ' secondary,' digestive process occurs in the caecum 
or in any other part of the large intestine. Probably any 
constituent of the food which has escaped digestion and 
absorption in the small bowel may be digested in the large 
intestine ; and the power of this part of the intestinal 
canal to digest fatty, albuminous, or other matters, may 
be gathered jfrom the good effects of nutrient enemata, so 
frequently given when from any cause there is difGLculty in 
introducing food into the stomach. In ordinary healthy 
digestion, however, the changes which ensue in the chyme 
after its passage into the large intestine, are mainly the 
absorption of the more liquid parts, and the addition of 
the special excretory products which give it the charac- 
teristic odour. At the same time, as before said, it is 
probable that a certain quantity of nutrient matter always 
escapes digestion in the small intestine, and that this 
happens more especially when food has been taken in 
excess, or when it is of such a kind as to be difficult of 
digestion. Under these circumstances there is no doubt 
that such changes as were proceeding in it at the lower 
part of the ileum may go on unchecked in the large bowel, 
— the process being assisted by the secretion of the nume- 
rous tubular glands therein present. 

By these means the contents of the large intestine, as 
they proceed towards the rectum, become more and more 
solid, and losing their more liquid and nutrient parts, 
gradually acquire the odour and consistence characteristic 



342 



DIGESTION. 



of faeces. After a sojourn of uncertain duration in the 
rectum, they are finally expelled by the contraction of its 
muscular coat, aided, under ordinary circumstances, by the 
contraction of the abdominal muscles. 

For a description of the mechanism by which the act of 
defaecation is accomplished, see p. 223. 

The average quantity of solid faecal matter evacuated by 
the human adult in twenty-four hours is about five ounces ; 
an uncertain proportion of which consists simply of the 
undigested or chemically modified residue of the food 
and the remainder of certain matters which are excreted 
in the intestinal canal. 



Composition of FcBces. 



"Water 
Solids 



733-00 
267*00 



Special excrementitious constituents : — Excretin, \ 
excretoleic acid (Marcet), and stercorin 
(Austin Flint). 

Salts : — Chiefly phosphate of magnesia and phos- 
phate of lime, with small quantities of iron, 
soda, lime, and silica. 

Insoluble residue of the food (chiefly starch, ; 
grains, woody tissue, particles of cartilage, 
and fibrous tissue, undigested muscular fibres 
or fat, and the like), with insoluble substances 
accidentally introduced with the food. 

Mucus, epithelium, altered colouring matter of 
bile, fatty acids, etc. 



267-00 



The time occupied by the journey of a given portion of 
food from the stomach to the anus, varies considerably even 
in health, and on this account, probably, it is that such 
difierent opinions have been expressed in regard to the 
subject. Dr. Brinton supposes twelve hours to be occupied 
by the journey of an ordinary meal through the small intes- 



GASES OF INTESTINAL CANAL. 343 

tine, and twenty-four to thirty-six hours by the passage 
through the large bowel. 



On the Gases contained in the Stomach and Intestines, 

It need scarcely be remarked that, under ordinary cir- 
cumstances, the alimentary canal contains a considerable 
quantity of gaseous matter. Any one who has had occa- 
sion, in a post-mortem examination, either to lay open the 
intestines, or to let out the gas which they contain, must 
have been struck by the smgdl space afterwards occupied 
by the bowels, and by the large degree, therefore, in which 
the gas, which naturally distends them, contributes to fill 
the cavity of the abdomen. Indeed, the presence of air in 
the intestines is so constant, and, within certain limits, the 
amount in health so uniform, that there can be no doubt 
that its existence here is not a mere accident, but intended 
to serve a definite and important purpose, although, pro- 
bably, a mechanical one. 

The sources of the gas contained in the stomach and 
bowels may be thus enumerated — 

1 . Air introduced in the act of swallowing either food or 
saliva. 

2. Gases developed by the decomposition of alimentary 
matter, or of the secretions and excretions mingled with it 
in the stomach and intestines. 

3. It is probable that a certain mutual interchange 
occurs between the gases contained in the alimentary 
canal, and those present in the blood of the gastric and in- 
testinal blood-vessels ; but the conditions of the exchange 
are not known, and it is very doubtful whether anything 
like a true and definite secretion of gas from the blood 
into the intestines or stomach ever takes places. There can 
be no doubt, however, that the intestines may be the 
proper excretory organs for many odorous and other sub- 
stances, either absorbed from the air taken into the lungs 



344 



DIGESTIOJ^. 



in inspiration, or absorbed in the upper part of the 
alimentary canal, again to be excreted at a portion of the 
same tract lower down — in either case assuming rapidly 
a gaseous form after their excretion, and in this way, 
perhaps, obtaining a more ready egress from the body. 

It is probable that, under ordinary circumstances, the 
gases of the stomach and intestines are derived chiefly from 
the second of the sources which have been enumerated. 

Tabular Analysis of Gases contained in the Alimentary Canal. 



Whence obtained. 


Composition by Volume. 








1 




Oxygen 


Nitrog. 


Carbon. 
Acid. 


TT_j„„ Carburet, 
^y^^ Hydrogen. 


Sulpburet 
Hydrogen. 


Stomach . . . 


II 


71 


14 


4 1 - 




Small Intestine . 




32 


30 


38 - 


\ 


Caecum .... 
Colon .... 


~ 


66 

35 


12 

57 


8 
6 


13 


> trace. 


Eectum. . . . 


— 


46 


43 


— II 


) 


Expelledi?er awwm 


— 


22 


41 


19 19 


I 



The above tabular analysis of the gases contained in the 
alimentary canal has been quoted from the analyses of 
Jurine, Magendie, Marchand, and Chevreul by Dr. Brinton, 
from whose work the above enumeration of the sources of 
the gas has been also taken. 



Movements oj the Intestines. 

It remains only to consider the manner in which the 
food and the several secretions mingled with it are 
moved through the intestinal canal, so as to be slowly 
subjected to the influence of fresh portions of intestinal 
secretion, and as slowly exposed to the absorbent power 
of all the villi and blood-vessels of the mucous mem- 
brane. The movement of the intestines is peristaltic 



MOVEMENTS OF THE INTESTINES. 345 

or vermicular, and is effected by the alternate con- 
tractions and dilatations of successive portions of tlie 
intestinal coats. The contractions, which may commence 
at any point of the intestine, extend in a wave-like 
manner along the tube. In any given portion, the longi- 
tudinal muscular fibres contract first, or more than the 
circular ; they draw a portion of the intestine upwards, or, 
as it were, backwards, over the substance to be propelled, 
and then the circular fibres of the same portion contracting 
in succession from above downwards, or, as it were, from 
behind forwards, press on the substance into the portion 
next below, in which at once the same succession of actions 
next ensues. These movements take place slowly, and, in 
health, are commonly unperceived by the mind ; but they 
are perceptible when they are accelerated under the influ- 
ence of any irritant. 

The movements of the intestines are sometimes retro- 
grade ; and there is no hindrance to the backward move- 
ment of the contents of the small intestine. But almost 
complete security is afforded against the passage of the 
contents of the large into the small intestine by the ileo- 
csecal valve. Besides, — the orifice of communication 
between the ileum and ceecum (at the borders of which 
orifice are the folds of mucous membrane which form 
the valve) is encircled with muscular fibres, the con- 
traction of which prevents the undue dilatation of the 
orifice. 

Proceeding from above downwards, the muscular fibres 
of the large intestine become, on the whole, stronger in 
direct proportion to the greater strength required for the 
onward moving of the faeces, which are gradually becoming 
firmer. The greatest strength is in the rectum, at the 
termination of which the circular unstriped muscular fibres 
form a strong band called the internal sphincter, while an 
external sphincter muscle with striped fibres is placed rather 
lower down, and more externally, and holds the orifice close 



346 DIGESTION. 

by a constant slight contraction under tlie influence of the 
spinal cord. 

The peculiar condition of the sphincter, in relation to the 
nervous system, will be again referred to. The remaining 
portion of the intestinal canal is under the direct influence 
of the sympathetic or ganglionic system, and indirectly, or 
more distantly, is subject to the influence of the brain and 
spinal cord, which influence appears to be, in some degree, 
transmitted through the vagus nerve. Experimental irri- 
tation of the brain or cord produces no evident or constant 
effect on the movements of the intestines during life ; yet 
in consequence of certain conditions of the mind, the move- 
ments are accelerated or retarded ; and in paraplegia the 
intestines appear after a time much weakened in their 
power, and costiveness, with a tympanitic condition, ensues. 
Immediately after death, irritation of both the sympathetic 
and pneumo-gastric nerves, if not too strong, induces 
genuine peristaltic movements of the intestines. Violent 
irritation stops the movements. These stimuli act, no 
doubt, not directly on the muscular tissue of the intestine, 
but on the rich ganglionic structure shown by Meissner to 
exist in the sub-mucous tissue. This regulates and controls 
the movements, and gives to them their peculiar slow, 
orderly, rhythmic, and peristaltic character, both naturally, 
and when artificially excited. 



347 



CHAPTER X. 



ABSOEPTION. 



The process of absorption has, for one of its objects, the 
introduction into the blood of fresh materials from the 
food and air, and of whatever comes into contact with the 
external or internal surfaces of the body ; and, for another, 
the taking away of parts of the body itself, when, having 
fulfilled their office, or otherwise requiring removal, they 
need to be renewed. In both these offices, i.e., in both 
absorption from without and absorption from within, the 
process manifests some variety, and a very wide range of 
action ; and in both it is probable that two sets of vessels 
are, or may be, concerned, namely, the blood-vessels, and 
the lacteals or lymphatics, to which the term absorbents 
has been especially applied. 

Structure and Office of the Lacteal and Lymphatic Vessels and 
Glands. 

Besides the system of arteries and veins, with their inter- 
mediate vessels, the capillaries, there is another system of 
canals in man and other vertebrata, called the lymphatic 
system, which contains a fluid called lymph. Both these 
systems of vessels are concerned in absorption. 

The principal vessels of the lymphatic system are, in 
structure and general appearance, like very small and thin- 
walled veins, and like them are provided with valves. By 
one extremity they commence by fine microscopic branches, 
the lymphatic^ capillaries or hjniph-capillaries, in the organs 
and tissues of nearly every part of the body, and by their 
other extremities they end directly or indirectly in two 
trunks which open into the large veins near the heart (fig. 
92). Their contents, the lymph smd chyle, unlike the blood, 



348 



ABSORPTION. 



pass only in one direction, namely, from the fine branches 
to the trunk and so to the large veins, on entering which 
they are mingled with the stream of blood, and form part 



Fig. 92.* 



Lymphatics of head 
and neck, right 



Right internal jug- 
ular vein. 
Right subcla-vian 
vein. 

Lymphatics of righ t 



Receptaculam chyli. 



Lymphatics of lower 
extremities. 




Lymphatics of head 
and neck, left. 

Thoracic duct 

Left suhclavian vein. 



Thoracic duct. 



Lymphatics of lowe 
extremities. 



of its constituents. Remembering the course of the fluid 
in the lymphatic vessels, viz., its passage in the direction 
only towards the large veins in the neighbourhood of the 
heart, it will be readily seen from fig. 92 that the greater 
part of the contents of the lymphatic system of vessels passes 



* Fig, 92. Diagram of the princii)al gi'oups of lymphatic vessels 
''from Quaiii). 



COUESE OF THE LYMPHATICS. 349 

through a comparatively large trunk called the thoracic 
duct, which finally empties its contents into the blood-stream 
at the junction of the internal jugular and subclavian veins 
of the left side. There is a smaller duct on the right side. 
The lymphatic vessels of the intestinal canal are called 
lacteals, because, during digestion, the fluid contained in 
them resembles milk in appearance ; and the lymph in the 
lacteals during the period of digestion is called chijle. 
There is no essential distinction, however, between lacteals 
and lymphatics. 

In some part of their course all lymphatic vessels pass 
through certain bodies called lymphatic glands. 

Lymphatic vessels are distributed in nearly all parts of 
the body. Their existence, however, has not yet been 
determined in the placenta, the umbilical cord, the mem- 
branes of the ovum, or in any of the non- vascular parts, 
as the nails, cuticle, hair, and the like. 

The lymphatic capillaries commence most commonly 
either in closely-meshed networks, or in irregular lacunar 
spaces between the various structures of which the dif- 
ferent organs are composed. The former is the rule of 
origin with those lymphatics which are placed most super- 
ficially, as, for instance, immediately beneath the skin, or 
under the mucous and serous membranes ; while the latter 
is most common with those which arise in the substance of 
organs. In the former instance, their walls are composed 
of but little more than homogeneous membrane, lined by 
a single layer of epithelial cells, very similar to those 
which line the blood-capillaries (fig. 49). In the latter 
instance the small irregular channels and spaces from 
which the lymphatics take their origin, although they are 
formed mostly by the chinks and crannies between the 
blood-vessels, secreting ducts, and other parts which may 
happen to form the framework of the organ in which they 
exist, yet have also a layer of epithelial cells to define and 
bound them. 



350 



ABSOEPTIOX. 



Tlie lacteals appear to offer an illustration of another 
mode of origin, namely, in blind dilated extremities (figs. 

Fig. 93-* 




* Fig. 93. Lymphatic vessels of the head and neck of the upper 
part of the tnink (from Mascagni). ^. — The chest and pericardium have 
been opened on the left side, and the left mamma detached and th^o■v^^^ 
outwards over the left arm, so as to expose a great part of its deep 
surface. The principal lymphatic vessels and glands are shown on the 
side of the head and face, and in the neck, axilla, and mediastinum. 
Between the left internal jugular vein and the common carotid artery, 
the upper ascending part of the thoracic duct marked i, and above 
this, and descending to 2, the arch and last part of the duct. The 
termination of the upper lymphatics of the diaphragm in the medi- 
astinal glands, as well as the cardiac and the deep mammary lymphatics, 
are also sho^vn. 



OEIGIX OF LYMPHATICS. 



351 



8 1, 82); but there is no essential difference in structure 
between these and the lymphatic capillaries of other parts, 
llecent discoveries seem likely to put an end soon to the 

Fig. 94.* 



Fig- 9S-t 





* Fig. 94. Superficial lymphatics of the forearm and pahn of the' 
hand, } (after Mascagni). 5. Two small glands at the bend of the- 
arm. 6. Radial lymphatic vessels. 7. Ulnar l}Tnpliatic vessels. 
8, 8. Palmar arch of lymphatics. 9, 9'. Outer and inner sets of vessels. 



352 ABSORPTION. 

long-standing discussion whether any direct communications 
exist between the lymph-capillaries and blood-capillaries ; 
the need for any special intercommunicating channels seem- 
ing to disappear in the light of more accurate knowledge of 
the structure and endowments of the parts concerned. For 
while, on the other hand, the fluid part of the blood con- 
stantly exudes or is strained through the walls of the blood- 
capillaries, so as to moisten all the surrounding tissues, 
and occupy the interspaces which exist among their 
different elements, these same interspaces have been shown, 
as just stated, to form the beginnings of the lymph-capil- 
laries. And while, for many years, the notion of the 
existence of any such channels between the blood-vessels 
and lymph- vessels, as would admit blood-corpuscles, has 
been given up, recent observations have proved that, for 
the passage of such corpuscles, it is not necessary to assume 
the presence of any special channels at all, inasmuch as 
blood-corpuscles can pass bodily, without much difficulty, 
through the walls of the blood-capillaries and small veins 
(p. 164), and could pass with still less trouble, probably, 
through the comparatively iU-defined walls of the capillaries 
which contain lymph. 

Observations of Recklinghausen have led to the dis- 
covery that in certain parts of the body openings exist 
by which lymphatic capillaries directly communicate with 
parts hitherto supposed to be closed cavities. If the peri- 
toneal cavity be injected with milk, an injection is obtained 
of the plexus of lymphatic vessels of the central tendon of 
the diaphragm ; and on removing a small portion of the 
central tendon, with its peritoneal surface uninjured, and 

h. Ceplialic vein. d. Radial vein. c. Median vein. /. Ulnar vein. 
The lymphatics are represented as lying on the deep fascia. 

+ Fig. 95. Superficial lymphatics of right gi-oin and upper part of 
thigh, ^ (after Mascagni). i. Upper inguinal glands. 2'. Lower in- 
guinal or femoral glands. 3, 3. Plexus of lymj)hatics in the course of 
the long saphenous vein. 



STRUCTURE OF LYMPHATIC VESSELS. 353 

>examiniiig the process of absorption under the micro- 
scope, Recklinghausen noticed that the milk -globules ran 
towards small natural openings or stomata between the 
epithelial cells, and disappeared by passing vortex-like 
through them. The stomata, which had a roundish outline, 
were only wide enough to admit two .or three milk-globules 
abreast, and never exceeded the size of an epithelial cell. 
Openings of a similar kind have been found by Dybskowsky 
in the pleura ; and as they may be presumed to exist in 
other serous membranes, it would seem as if the serous 
cavities, hitherto supposed closed, form but a large widen- 
ing out, so to speak, of the lymph-capillary system with 
which they directly communicate. 

In structure, the medium-sized and larger lymphatic 
vessels are very like veins ; having, according to Kolliker, 
an external coat of fibro-cellular tissue, with elastic 
filaments; within this, a thin layer of fibro-cellular 
tissue, with organic muscular fibres, which have, princi- 
pally, a circular direction, and are much more abundant in 
the small than in the larger vessels; and again, within 
this, an inner elastic layer of longitudinal fibres, and a 
lining of epithelium ; and numerous valves. The valves, 
constructed like those of veins, and with the free edges 
turned towards the heart, are usually arranged in pairs, 
and, in the small vessels, are so closely placed, that when 
the vessels are full, the valves constricting them where 
their edges are attached, give them a peculiar braided or 
knotted appearance (fig. 99). 

With the help of the valvular mechanism, all occasional 
pressure on the exterior of the lymphatic and lacteal ves- 
sels propels the lymph towards the heart : thus muscular 
•and other external pressure accelerates the flow of the 
lymph as it does that of the blood in the veins (see p. 1 70). 
The actions of the muscular fibres of the small intestine, 
and probably the layer of organic muscle present in each 
intestinal villus (p. 307), seem to assist in propelling the 



354 ABSORPTION. 

chyle : for, in the small intestine of a mouse, Poiseuille 
saw the chyle moving with intermittent propulsions that 
appeared to correspond with the peristaltic movements of 
the intestine. But for the general propulsion of the lymph 
and chyle, it is probable that, together with the vis a tergo 
resulting from absorption (as in the ascent of sap in 
a tree), and from external pressure, some of the force may 
be derived from the contractility of the vessel's own walls. 
Kolliker, after watching the lymphatics in the transparent 
tail of the tadpole, states that no distinct movements of 
their walls can ever be seen, but as they are emptied after 
death they gradually contract, and then, after some time, 
again dilate to their former size, exactly as the small 
arteries do under the like circumstances. Thus, also, the 
larger vessels in the human subject commonly empty 
themselves after death; so that, although absorption is 
probably usually going on just before the time of death, it 
is not common to see the lymphatic or lacteal vessels full. 
Their power of contraction under the influence of stimuli 
has been demonstrated by KoUiker, who applied the wire 
of an electro-magnetic apparatus to some well-filled 
lymphatics on the skin of a boy's foot, jujst after the re- 
moval of his leg by amputation, and noticed that the 
calibre of the vessels diminished at least one half. It is 
most probable that this contraction of the vessels occurs 
during life, and that it consists, not in peristaltic or undu- 
latory movements, but in an uniform contraction of the 
successive portions of the vessels, by which pressure is 
steadily exercised upon their contents, and which alternates 
with their relaxation. 

Lymphatic Glands. 

Almost all lymphatic and lacteal vessels in some part of 
their course pass through one or more small bodies called 
lymphatic glands (fig. 99). 

A lymphatic gland is covered externally by a capsule of 



LYMPHATIC GLANDS. 



355 




connective tissue, which invests and supports the glandular 
structure within ; while prolonged from its inner surface 
are processes or traheculcB which, entering the gland from 
all sides, and freely communicating, form a fibrous scaf- 
folding or stroma in all parts of the interior. Thus are 
formed in the outer or cortical part of the glands (fig. 96) 

in the intervals of the 

, , , , • . ^ Fig. 96.* 

trabeculse, certam inter- 
communicating spaces 
termed alveoli ; while 
a finer meshwork is 
formed in the more cen- 
tral or medullary part. 
In the alveoli and the 
trabecular meshwork the 
proper gland substance 
is contained ; in the form of nodules in the cortical alveoli, 
and of rounded cords in the medullary part (fig. 97). 
The gland -substance of one part is continuous directly 
or indirectly with that of all others. 

The essential structure of lymphatic-gland substance 
resembles that which was described as existing, in a simple 
form, in the interior of the solitary and agminated intes- 
tinal follicles (p. 302). Pervading all parts of it, and 
occupying the alveoli and trabecular spaces before referred 
to, is a network of the variety of connective tissue termed 
retiform tissue (fig. 98), the interspaces of which are 
occupied by lymph-corpuscles. The corpuscles are ar- 
ranged in such a way, that while in the centre of the 
alveoli and of each mesh they are so crowded together 
as to be, with the retiform tissue pervading them, a con- 

* Fig. 96 (after KoUiker). Section of a mesenteric gland from the. 
ox, slightly magnified, a, hilus ; h (in the central part of the figure), 
medullary substance ; c, cortical substance with indistinct alveoli ; cl, 
capsule. 



356 ABSOEPTION. 

sistent gland-pulp, continuous in the form, of the nodules 
and cords, before referred to, throughout the whole gland, 
they are in comparatively small numbers in the outer part 
of the alveoli and meshes, and leave this portion, as it 
were, open. (See figs. 97, 98.) This free space between 
the gland-pulp and the trabecular stroma, occupied only by 
retiform tissue, is called the lymph-channel or lymph -path, 
because it is traversed by the lymph, which is continually 
brought to the gland and conveyed away from it by 

Fij. 97.* 




lymphatic vessels ; those which bring it being termed 
afferent vessels, and those which take it away efferent 
vessels. The former enter the cortical part of the gland 
and open i?ito its alveoli, at the same time that they lay 
aside all their coats except the epithelial lining, which may 
be said to continue to line the lymph-path into which the 

* Fig. 97. Section of Medullary Substance of an Inguinal Gland 
of an Ox (magnified 90 diameters), a, a, glandular substance or 
pulp forming rounded cords joining in a continuous net (dark in the 
figure) ; c, c, trabeculaj ; tlie space, b, b, between these and the gland- 
ular substance is the lymph-sinus, ■washed clear of corpuscles and 
traversed by filaments of retiform connective tissue (after Kolliker). 



LYMPHATIC GLAXDS. 



357 



contents of the afferent vessels now pass. The ^ 
vessels begin in the medullary part of the gland, and are 
continuous with the lymph-path here as the a f event vessels 
were with the cortical portion ; the epithelium of one is 
continuous with that of the other. 

Blood-vessels are freely distributed to the trabecular 
tissue and to the gland-pulp (fig. 98). 

Properties of Lymph and Chyle. 

The fluid, or lymph, contained in the lymphatic vessels 
Fiff. 98* 




is, under ordinary circumstances, clear, transparent, and 

* Fig, 98. A Small Portion of Medullary Substance from a Mesen- 
teric Gland of tlie Ox (magnified 300 diameters), d, d, trabecular ; a, 
j)art of a cord of glandular substances from which all but a few of 
the lymph-corpuscles have been washed out to show its supporting 
meshwork of retiform tissue and its capillary blood-vessels (which have 
been injected, and are dark in the figure) ; &, h, lymph-sinus, of which 
the retiform. tissue is represented only at c, c (after Kolliker). 



358 



ABSOEPTION. 



colourless, or of a pale yellow tint. It is devoid of smell, 
is slightly alkaline, and has a saline taste. As seen with 
the microscope in the small transparent vessels of the tail 
of the tadpole, the lymph usually contains no corpuscles or 
particles of any kind ; and it is probably only in the larger 
trunks in which, by a process similar to that to be described 
in the chyle, the lymph is more elaborated, that any cor- 
Fig. 99.* puscles are formed. These corpuscles are 
similar to those in the chyle, but less nume- 
rous. The fluid in which the corpuscles float 
is commonly and in health albuminous, and 
contains no fatty particles or molecular base ; 
but it is liable to variations according to the 
general state of the blood, and that of the 
organ from which the lymph is derived. As 
it advances towards the thoracic duct, and 
passes through the lymphatic glands, it be- 
comes, like chyle, spontaneously coagulable 
from the formation of fibrin, and the number 
of corpuscles is much increased. 

The fluid contained in the lacteals, or 
lymphatic vessels of the intestine, is clear 
and transparent during fasting, and differs 
in no respect from ordinary lymph; but 
during digestion, it becomes milkj^, and is 
termed chyle. 

Chyle is an opaque, whitish fluid, resem- 
bling milk in appearance, and having a neu- 
tral or slightly alkaline reaction. Its white- 
ness and opacity are due to the presence 
of innumerable particles of oily or fatty matter, of exceed- 
ingly minute though nearly uniform size, measuring on the 
average about -rohro o^ an inch (Gulliver). These con- 
stitute what Mr. Gulliver appropriately terms the molecular 

* ^ig- 99' -^ lymiiliatic gland from the axilla, with its afferent and 
efferent vessels, injected with mercury (after Bendz). 





CHYLE. 



359 



base of chyle. Their number, and consequently the opacity 
of the chyle, are dependent upon the quantity of fatty 
matter contained in the food. Hence, as a rules, the chyle 
is whitish and most turbid in carnivorous animals ; less so 
in Herbivora ; while in birds it is usually transparent. 
The fatty nature of the molecules is made manifest by 
their solubility in ether, and, when the ether evaporates, 
by their being deposited in various-sized drops of oil."^'- 
Yet, since they do not run together and form a larger 
drop, as particles of oil would, it appears very probable 
that each molecule consists of oil coated over with albu- 
men, in the manner in which, as Ascherson observed, oil 
always becomes covered when set free in minute drops in 
an albuminous solution. And this view is supported by 
the fact, that when water or dilute acetic acid is added to 
chyle, many of the molecules are lost sight of, and oil- 
drops appear in their place, as if the investments of the 
molecules had been dissolved, and their oily contents had 
run together. 

Except these molecules, the chyle taken from the villi 
or from lactoals near them, contains no other solid or 
organized bodies. The fluid in which the molecules float 
is albuminous, and does not spontaneously coagulate, 
though coagulable by the addition of ether. But as the 
chyle passes on towards the thoracic duct, and especially 
while it traverses one or more of the mesenteric glands 
(propelled by forces which have been described with the 
structure of the vessels), it is elaborated. The quantity of 
molecules and oily particles gradually diminishes ; cells, to 
which the name of chyle-corpuscles is given, are developed 
in it J and by the formation of fibrin, it acquires the pro- 
perty of coagulating spontaneously. The higher in the 



* Some of the molecules may remain undissolved by tlie ether ; but 
this appears to be due to their being defended from the action of the 
ether by being entangled within the albumen which it coagulates. 



360 ABSORPTION. 

thoracic duct the chyle advances, the more is it, in all 
these respects, developed; the greater is the number of 
chyle-corpuscles, and the larger and firmer is the clot 
which forms in it when withdrawn and left at rest. Such 
a clot is like one of blood, without the red corpuscles, 
having the chyle-corpuscles entangled in it, and the fatty 
matter forming a white creamy film on the surface of the 
serum. But the clot of chyle is softer and moister than 
that of blood. Like blood, also, the chyle often remains 
for a long time in its vessels without coagulating, but 
coagulates rapidly on being removed from them (Bouisson). 
The existence of fibrin, or of the materials which, by their 
union form it (p. 65 et seq.), is, therefore, certain; its 
increase appears to be commensurate with that of the 
corpuscles ; and, like them, it is not absorbed as such from 
the chyme (for no fibrin exists in the chyle in the villi), 
but is gradually elaborated out of the albumen which chyle, 
in its earliest condition, contains. 

The structure of the chyle- corpuscles was described 
when speaking of the white corpuscles of the blood, with 
which they are identical. 

From what has been said, it will appear that perfect 
chyle and lymph are, in essential characters, nearly similar, 
and scarcely differ, except in the preponderance of fatty 
matter in the chyle. The comparative analysis of the two 
fluids obtained from the lacteals and the lymphatics of a 
donkey is thus given by Dr. Owen Bees : — 

Chyle. Ljnnpli. 

Water 90-237 96-536 

Albumen . . . . . . 3 "5 16 i-2cxd 

Fibrin 0370 0-120 

Animal extractive 1*565 i"559 

Fatty matter 3-601 a trace. 

Salts 0-71 1 0-585 



loo'ooo 100-000 
The analyses of Nasse afford an estimate of the rela- 



COMPOSITION OF LYMPH AND CHYLE. 36 1 



tive compositions 


of the 


lymph, chyle, and blood of the 


horse."' 














Lymph. 


Chyle. 


Blood. 


AVatcr . 


. 


950- 


935' 


8io- 


('orpuscles . 






4' 


92-8 


Albumen 




39-11 


31 ' 


So- 


Fibrin 






075 


2-8 


Extractive matter 


. 


4-S8 


6-25 


5-2 


Fatty matter 




0-09 


15- 


155 


Alkaline salts 




5-6i 


r 


67 


Phosphate of lime and mag- 
nesia, oxide of iron, etc. 


1- 0.3. 


I* 


0-95 



The contents of the thoracic duct, including both the 
lyraph and chyle mixed, in an executed criminal, were 
examined by Dr. Rees, who found them to consist of — 

AVater 90*48 

Albumen and fibrin 7 "08 

Extractive matter . . . . . . . o'io8 

Fatty ,, 0-92 

Saline ,, 0-44 

From all these analyses of lymph and chyle, it appears 
that they contain essentially the same organic constituents 
that are found in the blood, viz., albumen, fibrin, and fatty 
matter, the same saline substances, and iron. Their com- 
position difi'ers from that of the blood in degree rather than 
in kind ; they contain a less proportion of all the substances 
dissolved in the water (see Nasse's analyses, just quoted), 
and much less fibrin. The fibrin f of lymph, besides being 
less in quantity, appears to be in a less elaborated state 
than that of the blood, coagulating less rapidly and less 
firmly. According to Virchow, it never coagulates, under 

* The analysis of the blood differs rather widely from that given at 
page 78 ; but if it be erroneous, it is probable that corresponding errors 
exist in the analysis of the lymph and chyle ; and that therefore the 
tables in the text may represent accurately enough the relation in which 
the three fluids stand to each other. 

t For obseiTations on the nature of fibrin, see p. 6^. 



362 ABSORPTION. 

ordinary circumstances, within the lymphatic vessels, either 
during life or after death. These differences gradually 
diminish, while the lymph and chyle, passing towards and 
through the thoracic duct, gradually approach the place at 
which they are to be mingled with the blood. For, in the 
thoracic duct, besides the higher and more abundant 
development of the fibrin, the lymph and chyle-corpuscles 
are found more advanced towards their development into 
red-blood corpuscles ; sometimes even that development is 
completed, and the lymph has a pinkish tinge from the 
number of red blood-corpuscles that it contains. 

The general result, therefore, of both the microscopic 
and the chemical examinations of the lymph and chyle, 
demonstrate that they are rudimental blood; their fluid 
part being, like the liquor sanguinis, diluted, but gradually 
becoming more concentrated ; and their corpuscles being 
in process of development into red blood-corpuscles. Thus^ 
in quality, the lymph and chyle are adapted to replenish 
the blood ; and their quantity, so far as it can be estimated, 
appears ample for this purpose. In one of Magendie's 
experiments, half an ounce of chyle was collected in five 
minutes from the thoracic duct of a middle-sized dog ; 
Collard de Martigny obtained nine grains of lymph, in ten 
minutes from the thoracic duct of a rabbit which had 
taken no food for twenty-four hours ; and Gieger, from 
three to five pounds of lymph daily from the foot of a 
horse, from whom the same quantity had been flowing 
several yeafrs without injury to health. Bidder found, on 
opening the thoracic duct in cats, immediately after death, 
that the mingled lymph and chyle continued to flow from 
one to six minutes ; and, from the quantity thus obtained, 
he estimated that if the contents of the thoracic duct con- 
tinued to move at the same rate, the quantity which would 
pass into a cat's blood in twenty-four hours would be equal 
to about one-sixth of the weight of the whole body. And, 
since the estimated weight of the blood in cats is to the 



QUANTITY OF LYMPH AND CHYLE. 363 

weight of their bodies as I : 7, the quantity of lymph daily 
traversing the thoracic duct would appear to be about 
equal to the quantity of blood at any time contained in the 
animals. Schmidt's observations on foals have yielded 
very similar results. By another series of experiments, 
Bidder estimated that the quantity of lymph traversing 
the thoracic duct of a dog in twenty-four hours is about 
equal to two -thirds of the blood in the body. If we take 
these estimates, it will not follow from them that the whole 
of an animal's blood is daily replaced by the development 
of lymph and chyle ; for even if the quantity of lymph 
and chyle daily formed be equal to that of the blood, the 
solid contents of the blood will be much too great to be 
replaced by those of the lymph and chyle. According to 
Nasse's analyses, the solid matter of a given quantity of 
blood could not be replaced out of less than three or four 
times the quantity of lymph and chyle. 

Absorption by the Lacteal Vessels. 

During the passage of the chyme along the whole tract 
of the intestinal canal, its completely digested parts are 
absorbed by the blood-vessels and lacteals distributed in 
the mucous membrane. The blood-vessels appear to 
absorb chiefly the dissolved portions of the food, and 
these, including especially the albuminous and saccharine, 
they imbibe without choice ; whatever can mix with the 
blood passes into the vessels, as will be presently described. 
But the lacteals appear to absorb only certain constituents 
of the food, including particularly the fatty portions. The 
absorption by both sets of vessels is carried on most 
actively, but not exclusively, in the villi of the small intes- 
tine; for in these minute processes, both the capillary 
blood-vessels and the lacteals are brought almost into 
contact with the intestinal contents. 

It has been already stated that the villi of the small 
intestine (figs. 81 and 82), are minute vascular processes 



364 ABSOEPTIOK 

of mucous membrane, each containing a delicate net- 
work of blood-vessels and one or more lacteals, and are 
invested by a sbeatli of cylindrical epithelium. In the 
interspaces of the mucous membrane between the villi, as 
well as over all the rest of the intestinal canal, the lacteals 
and blood-vessels are also densely distributed in a close net- 
work, the lacteals, however, being more sparingly supplied 
to the large than to the small intestine. 

There seems to be no doubt that absorption of fatty 
matters during digestion, from the contents of the intes- 
tines, is effected chiefly by the epithelial cells which line 
the intestinal tract, and especially by those which clothe 
the surface of the villi (fig. 81). From these epithelial 
cells, again, the fatty particles are passed on into the inte- 
rior of the lacteal vessels (figs. 81 and 82), but how they 
pass, and what laws govern their so doing, are not at pre- 
sent exactly known. 

It is probable that the process of absorption by the epi- 
thelial cells, is assisted by the pressure exercised on the 
contents of the intestines by their contractile walls ; and 
that the absorption of fatty particles is also facilitated by 
the presence of the bile, the pancreatic and intestinal se- 
cretions which moisten the absorbing surface. For it has 
been found by experiment, that the passage of oil through 
an animal membrane is made much easier when the latter 
is impregnated with an alkaline fluid. 

Absorption by the Lymphatic Vessels. 

The real source of the lymph, and the mode in which its 
absorption is effected by the lymphatic vessels, were 
long matters of discussion. But the problem has been 
much simplified by more accurate knowledge of the anato- 
mical relations of the lymphatic capillaries. It is most 
probable that the lymph is derived, in great part, from the 
liquor sanguinis, which, as before remarked, is always 
exuding from the blood-capillaries into the interstices of 



ABSOEPTIOX BT LYMPHATICS. 



165 



the tissues in which they lie ; and changes in the cha- 
racter of the lymph correspond very closely with changes 
in the character of either the whole mass of blood, or of 
that in the vessels of the part from which the lymph is 
examined. Thus Herbst found that the coagulability of 
the lymph is directly proportionate to that of the blood ; 
and that when fluids are injected into the blood-vessels 
in sufficient quantity to distend them, the injected sub- 
stance may be almost directly afterwards found in the 
lymphatics. 

It is not improbable, however, that some other matters 
than those originally contained in the exuded liquor san- 
guinis may find their way with it into the lymphatic 
vessels. Parts which having entered into the composition 
of a tissue, and, having fulfilled their purpose, require to 
be removed, may not be altogether excrementitious, but 
may admit of being re-organised and adapted again for 
nutrition ; and these may be absorbed by the lymphatics, 
and elaborated with the other contents of the lymph in 
passing through the glands. 

Lymph-Hearts. In reptiles and some birds, an important 
auxiliary to the movement of the lymph and chyle is sup- 
plied in certain muscular sacs, named lymph-hearts (fig. lOO), 
and Mr. Wharton Jones has lately shown that the caudal 
heart of the eel is a lymph-heart also. The number and 
position of these organs vary. In frogs and toads there 
are usually four, two anterior and two posterior ; in the 
frog, the posterior lymph-heart on each side is situated in 
the ischiatic region, just beneath the skin ; the anterior 
lies deeper, just over the transverse process of the third 
vertebra. Into each of these cavities several lymphatics 
open, the orifices of the vessels being guarded by valves, 
which prevent the retrograde passage of the lymph. From 
each heart a single vein proceeds and conveys the lymph 
directly into the venous system. In the frog, the inferior 
lymphatic heart, on each side, pours its lymph into a 




366 ABSOEPTIOX. 

brancli of the ischiatic vein ; by tlie superior, the lympli 

is forced into a branch of the 
Fig. 100 * jugular vein, which issues from 

its anterior surface, and which 
becomes turgid each time that 
the sac contracts. Blood is pre- 
vented from passing from the 
vein into the lymphatic heart by 
a valve at its orifice. 

The muscular coat of these 
hearts is of variable thickness; 
in some cases it can only be dis- 
covered by means of the micro- 
scope; but in every case it is composed of transversely- 
striated fibres. The contractions of the hearts are rhyth- 
mical, occurring about sixty times in a minute, slowly, and, 
in comparison with those of the blood-hearts, feebly. 
The pulsations of the cervical pair are not always synchro- 
nous with those of the pair in the ischiatic region, and 
even the corresponding sacs of opposite sides are not always 
synchronous in their action. 

Unlike the contractions of the blood-heart, those of the 
lymph-heart appear to be directly dependent upon a cer- 
tain limited portion of the spinal cord. For Volkmann 
found that so long as the portion of spinal cord correspond- 
ing to the third vertebra of the frog was uninjured, the 
cervical pair of lymphatic hearts continued pulsating after 
all the rest of the spinal cord and the brain was destroyed ; 
while destruction of this portion, even though alT other 

* Fig. ICO. Lymphatic heart (9 lines long, 4 lines broad) of a large 
species of serpent, the Python bivittatus (after E. "Weber). 4. The 
external cellular coat. 5. The thick muscular coat. Four muscular 
columns run across its cavity, which communicates vdi\\ three lymj)ha- 
tics (i — only one is seen here), with two veins (2, 2). 6. The smooth 
hning membi-ane of the cavity. 7. A small appendage, or auricle, the 
cavity of which is continuous with that of the rest of the organ. 



ABSOEPTION BY BLOOD-VESSELS. 367 

parts of the nervous centres were uninjured, instantly- 
arrested the heart's movements. The posterior or ischiatic 
pair of lymph-hearts were found to be governed, in like 
manner, by the portion of spinal cord corresponding to 
the eighth vertebra. Division of the posterior spinal roots 
did not arrest the movements ; but division of the anterior 
roots caused them to cease at once. 

Absorption by Blood-vessels. 

The process thus named is that which has been com- 
monly called absorption by the veins ; but the term here 
employed seems preferable, since, though the materials 
absorbed are commonly found in the veins, this is only 
because they are carried into them with the circulating 
blood, after being absorbed by all the blood-vessels (but 
chiefly by the capillaries) with which they were placed in 
contact. There is nothing in the mode of absorption by 
blood-vessels, or in the structure of veins, which can make 
the latter more active than arteries of the same size, or so 
active as the capillaries, in the process. 

In the absorption by the lymphatics or lacteal vessels 
just described, there appears something like the exercise 
of choice in the materials admitted into them. But the 
absorption by blood-vessels presents no such appearance 
of selection of materials; rather, it appears that every 
substance, whether gaseous, liquid, or a soluble or minutely 
divided solid, may be absorbed by the blood-vessels, pro- 
vided it is capable of permeating their walls, and of 
mixing with the blood ; and that of all such substances, 
the mode and measure of absorption are determined solely 
by their physical or chemical properties and conditions, and 
by those of the blood and the walls of the blood-vessels. 

The phenomena are, indeed, exactly comparable to that 
passage of fluids through membrane, which occurs quite 
independently of vital conditions, and the earliest and best 
scientific investigation of which was made by Dutrochet. 



368 



ABSORPTION. 



Fig. loi. 



The instrument whicli he employed in his experiments was 
named an endosmometer. It may consist of a graduated 
tube expanded into an open-mouthed bell 
at one end, over which a portion of mem- 
brane is tied (fig. loi). If now the bell be 
filled with a solution of a salt — say chloride 
of sodium, and be immersed in water, the 
water will pass into the solution, and jjart 
of the salt will pass out into the water ; the 
water will pass into the solution, much more 
rapidly than the salt will pass out into the 
water, and the diluted solution will rise in 
the tube. To this passage of fluids through 
membrane the term Osmosis is applied. 

The nature of the membrane used as a 
septum, and its affinity for the fluids sub- 
jected to experiment have an important 
influence, as might be anticipated, on the 
rapidity and duration of the osmotic current. 
Thus, if a piece of ordinary bladder be used 
as the septum between water and alcohol, the current is 
almost solely from the water to the alcohol, on account of 
the much greater affinity of water for ' this kind of mem- 
brane ; while, on the other hand, in the case of a membrane 
of caoutchouc, the alcohol, from its greater affinity for this 
substance, would pass freely into the water. 

Various opinions have been advanced in regard to the 
nature of the force by which fluids of different chemical 
composition thus tend to mix through an intervening 
membrane. According to some, this power is the result 
of the different degrees of capiUary attraction exerted by 
the pores of the membrane upon the two fluids. Prof. 
Graham, however, believes that the passage or osmose of 
water through membrane may be explained by supposing 
that it combines with the membranous septum, which thus 
becomes hydrated, and that on reaching the other side it 
partly leaves the membrane, which thus becomes to a 




COLLOIDS AND CRYSTALLOIDS. 369 

certain degree de-hydrated. For example, a membrane 
such, as that used in the endosmometer, is hydrated to a 
higher degree if placed in pure water than in a neutral 
saline solution. Hence, in the case of the endosmometer 
filled with the saline solution and placed in water, the 
equilibrium of hydration is different on the two sides ; 
the outer surface being in contact with pure water tends 
to hydrate itself in a higher degree than the inner surface 
does. '' When the full hydration of the outer surface ex- 
tends through the thickness of the membrane, and reaches 
the inner surface, it there receives a check. The degree of 
hydration is lowered, and water must be given up by 
the inner layer of the membrane." Thus the osmose or 
current of water through the membrane is caused. The 
passage outwards of the saline solution, on the other hand, 
is not due, probably, to any actual Jluid current ; but^to^a 
solution of the salt in successive layers of the water con- 
tained in the pores of the membrane, until it reaches the 
outer surface and diffuses in the water there situate. 

Thus, '' the water movement in osmose is an affair of 
hydration and of de-hydration in the substance of the 
membrane or other colloid septum, and the diffusion of the 
saline solution placed within the osmometer has little or 
nothing to do with the osmotic result, otherwise than as it 
affects the state of hydration of the septum." 

Prof. Graham has classed various substances according 
to the degree in which they possess this property of passing, 
when in a state of solution in water, through membrane ; 
those which pass freely being termed crystalloids, and those 
which pass with difficulty, colloids. 

This distinction, however, between colloids and crystal- 
loids which is made the basis of their classification, is 
by no means the only difference between them. The 
colloids, besides the absence of power to assume a crystal- 
line form, are characterised by their inertness as acids or 
bases, and feebleness in all ordinary chemical relations. 
Examples of them are found in albumen, gelatin, starch, 

B B 



370 ABSORPTION. 

hydrated alumina, hydrated silicic acid, etc. ; while the 
crystalloids are characterised by qualities the reverse of 
those just mentioned as belonging to colloids. Alcohol, 
sugar, and ordinary saline substances are examples of 
crystalloids. 

Absorption by blood-vessels is the consequence of their 
walls being, like the membranous septum of the endos- 
mometer, porous and capable of imbibing fluids, and of 
the blood being so composed that most fluids will mingle 
with it. The process of absorption, in an instructive, 
though very imperfect degree, may be observed in any 
portion of vascular tissue removed from the body. If such 
an one be placed in a vessel of water, it will shortly swell, 
and become heavier and moister, through the quantity of 
water imbibed or soaked into it ; and if now, the blood 
contained in any of its vessels be let out, it will be found 
diluted with water, which has been absorbed by the blood- 
vessels and mingled with the blood. The water round the 
piece of tissue also will become blood-stained ; and if aU 
be kept at perfect rest, the stain derived from the solution 
of the colouring matter of the blood (together with which 
chemistry w^ould detect some of the albumen and other 
parts of the liquor sanguinis) will spread more widely 
every day. The same will happen if the piece of tissue be 
placed in a saline solution instead of water, or in a solution 
of colouring or odorous matter, either of which wdll give 
their tinge or smell to the blood, and receive, in exchange, 
the colour of the blood. 

Even so simple an experiment will illustrate the ab- 
sorption by blood-vessels during life ; the process it shows 
is imitated, but with these differences : that, during life, 
as soon as water or any other substance is admitted into 
the blood, it is carried from the place at which it was 
absorbed into the general current of the circulation, and 
that the colouring matter of the blood is not dissolved so 
as to ooze out of the blood-vessels into the fluid which they 
^re absorbing:. 



EAPIDITY OF ABSORPTIOX. 371 

The absorption of gases by the blood may be thus simply 
imitated. If venous blood be suspended in a moist bladder 
in the air, its surface will be reddened by the contact of 
oxygen, which is first dissolved in the fluid that moistens 
the bladder, and is then carried in the fluid to the surface 
of the blood : while, on the other hand, watery vapour 
and carbonic acid wiU pass through the membrane, and be 
exhaled into the air. 

In all these cases alike there is a mutual interchange be- 
tween the substances ; while the blood is receiving water, 
it is giving out its colouring matter and other constituents : 
or, while it is receiving oxygen, it is giving out carbonic 
acid and water ; so that, at the end of the experiment, the 
two substances employed in it are mixed ; and if, instead 
of a piece of tissue, one had taken a single blood-vessel 
full of blood and placed it in the water, both blood and 
water would, after a time, have been found both inside and 
outside the vessel. In such a case, moreover, if one were 
to determine accurately the quantity of water that passed 
to the blood, and of blood that "passed to the water, it 
would be fourd that the former was always greater than 
the latter. And so with other substances; it almost always 
happens, that if the two liquids placed on opposite sides of 
a membrane be of difi'erent densities or specific gravities, 
a larger quantity of the less dense fluid passes into the 
more dense, than of the latter into the former. 

The rapidity with which matters may be absorbed from 
the stomach probably by the blood-vessels chiefly, and dif- 
fused through the textures of the body, may be gathered 
from the history of some experiments by Dr. Bence Jones. 
From these it appears that even in a quarter of an hour 
after being given on an empty stomach, chloride of lithium 
may be diffused into all the vascular textures of the body, 
and into some of the non-vascular, as the cartilage of the 
hip-joint, as well as into the aqueous humour of the eye. 
Into the outer part of the crystalline lens it may pass after 
a time, varying from half an hour to an hour and a half. 

B B 2 



372 



ABSORPTIOX. 



Carbonate of lithia, when taken in five or ten grain doses 
on an empty stomaeli, may be detected in the urine in 5 or 
10 minutes ; or, if the stomach be full at the time of taking 
the dose, in 20 minutes. It may sometimes be detected in 
the urine, moreover, for six, seven, or even eight days. 

Some experiments on the absorption of various mineral 
and vegetable poisons, by Mr. Savory, have brought to light 
the singular fact, that, in some cases, absorption takes place 
more rapidly from the rectum than from the stomach. 
Strychnia, for example, when in solution, produces its 
poisonous effects much more speedily when introduced into 
the rectum than into the stomach. When introduced in 
the solid form, however, it is absorbed more rapidly from 
the stomach than from the rectum, doubtless because of 
the greater solvent property of the secretion of the former 
than of that of the latter. 

With regard to the degree of absorption by living blood- 
vessels, much depends on the facility with which the sub- 
stance to be absorbed can penetrate the membrane or tissue 
which lies between it and the blood-vessels ; for, naturally, 
the blood-vessels are not bare to absorb. Thus absorption 
will hardly take place through the epidermis, but is quick 
when the epidermis is removed, and the same vessels are 
covered with only the surface of the cutis, or with granula- 
tions. In general, the absorption through membranes is in 
an inverse proportion to the thickness of their epithelia ; 
so Miiller found the urinary bladder of a frog traversed in 
less than a second ; and the absorption of poisons by the 
stomach or lungs appears sometimes accomplished in an 
immeasurably small time. 

The substance to be absorbed must, as a general rule, be 
in the liquid or gaseous state, or, if a solid, must be soluble 
in the fluids with which it is brought in contact. Hence 
the marks of tattooing, and the discoloration produced by 
nitrate of silver taken internally, remain. Mercury may 
be absorbed even in the metallic state ; and in that state 
may pass into and remain in the blood-vessels, or be 



ABSORPTION BY BLOOD-VESSELS. 373 

deposited from them (Oesterlen) ; and such substances as 
exceedingly finely-divided charcoal, when taken into the 
alimentary canal, have been found in the mesenteric veins 
(Oesterlen) ; the insoluble materials of ointments may also 
be rubbed into the blood-vessels ; but there are no facts to 
determine how these various substances effect their pass- 
age. Oil, minutely divided, as in an emulsion, will pass 
slowly into blood-vessels, as it will through a filter mois- 
tened with water (Vogel); and, without doubt, fatty matters 
find their way into the blood-vessels as well as the lymph- 
vessels of the intestinal canal, although the latter seem to 
be specially intended for their absorption. 

As in the experiments before referred to, the less dense 
the fluid to be absorbed, the more speedy, as a general 
rule, is its absorption by the living blood-vessels. Hence 
the rapid absorption of water from the stomach; also of 
weak saline solutions ; but with strong solutions, there 
appears less absorption into, than effusion from, the blood- 
vessels. 

The absorption is the less rapid the fuller and tenser the 
blood-vessels are ; and the tension may be so great as 
to hinder altogether the entrance of more fluid. Thus, 
Magendie found that when he injected water into a dog's 
veins to repletion, poison was absorbed very slowly; but 
when he diminished the tension of the vessels by bleeding, 
the poison acted quickly. So, when cupping-glasses are 
placed over a poisoned wound, they retard the absorption 
of the poison, not only by diminishing the velocity of the 
circulation in the part, but by filling all its vessels too full 
to admit more. 

On the same ground, absorption is the quicker the more 
rapid the circulation of the blood ; not because the fluid 
to be absorbed is more quickly imbibed into the tissues, or 
mingled with the blood, but because as fast as it enters 
the blood, it is carried away from the part, and the blood, 
being constantly renewed, is constantly as fit as at the first 
for the reception of the substance to be absorbed. 



374 



CHAPTER XI. 



NUTKITTON AND GROWTH. 



Nutrition' or nutritive assimilation is that modification 
of the formative process peculiar to living bodies by which 
tissues and organs already formed maintain their integrity. 
By the incorporation of fresh nutritive principles into their 
substance, the loss consequent on the waste and natural 
decay of the component particles of the tissues is repaired ; 
and each elementary particle seems to have the power not 
only of attracting materials from the blood, but of causing 
them to assume its structure, and participate in its vital 
properties. 

The relations between development and growth have 
been already stated (Chap. I.) ; imder the head of Nutri- 
tion will be now considered the process by which parts 
are maintained in the same general conditions of form, 
size, and composition, which they have already, by develop- 
ment and growth, attained; and this, notwithstanding 
continual changes in their component particles. It is 
by this process that an adult person, in health, is main- 
tained, through a series of some years, with the same 
general outline of features, the same size and form, and 
perhaps even the same weight ; although, during all this 
time, the several portions of his body are continually 
changing : their particles decaying and being removed, 
and then replaced by the formation of new ones, which, 
in their turn, also die and pass away. Neither is it only 
a general similarity of the whole body which is thus main- 
tained. Every organ or part of the body, as much as the 
whole, exactly maintains its form and composition, as 



NUTRITIOX, 



375 



the issue of tlie changes continually taking place among 
its particles. 

The change of component particles, in which the nutri- 
tion of organs consists, is most evidently shown when, in 
growth, they maintain their form and other general charac- 
ters, but increase in size. When, for example, a long 
bone increases in circumference, and in the thickness of 
its walls, while, at the same time, its medullary cavity 
enlarges, it can only be by the addition of materials to its 
exterior, and a coincident removal of them from the 
interior of its wall ; and so it must be with the growth of 
even the minutest portions of a tissue. And that a similar 
change of particles takes place, even while parts retain a 
perfect uniformity, may be proved, if it can be shown that 
all the parts of the body are subject to waste and impair- 
ment. 

In many parts, the removal of particles is evident. 
Thus, as will be shown when speaking of secretion, the 
elementary structures composing glands are the parts of 
which the secretions are composed : each gland is con- 
stantly casting off its cells, or their contents, in the 
secretion which it forms : yet each gland maintains its 
size and proper composition, because for every cell cast off 
a new one is produced. So also the epidermis and all 
such tissues are maintained. In the muscles, it seems 
nearly certain, that each act of contraction is accompanied 
with a change in the composition of the contracting tissue, 
although the change from this cause is less rapid and 
extensive than was once supposed. Thence, the develop- 
ment of heat in acting muscles, and thence the discharge 
of urea, carbonic acid, and water — the ordinary products 
of the (decomposition of the animal tissues — which fol- 
lows all active muscular exercise. Indeed, the researches 
of Helmholtz almost demonstrate the chemical change 
that muscles undergo after long-repeated contractions ; 
yet the muscles retain their structure and composition^ 



^^j6 NUTEITIOX. 

because the particles thus changed are replaced by 
new ones resembling those which preceded them. So 
again, the increase of alkaline phosphates discharged with 
the urine after great mental exertion, seems to prove that 
the various acts of the nervous system are attended with 
change in the composition of the nervous tissue ; yet the 
condition of that tissue is maintained. In short, for every 
tissue there is sufficient evidence of impairment in the 
discharge of its functions : without such change, the pro- 
duction or resistance of physical force is hardly conceivable : 
and the proof as well as the purpose of the nutritive pro- 
cess appears in the repair or replacement of the changed 
particles ; so that, notwithstanding its losses, each tissue 
is maintained unchanged. 

But besides the impairment and change of composition 
to which all parts are subject in the discharge of their 
natural functions, an amount of impairment which will be 
in direct proportion to their activity, they are all liable to 
decay and degeneration of their particles, even while their 
natural actions are not called forth. It may be proved, 
as Dr. Carpenter first clearly showed, that every particle 
of the body is formed for a certain period of existence in 
the ordinary condition of active life ; at the end of which 
period, if not previously destroyed by outward force or 
exercise, it degenerates and is absorbed, or dies and is 
cast out. 

The simplest examples that can be adduced of this are 
in the hair and teeth ; and it may be observed, that, in 
the process which will now be described, all the great 
features of the process of nutrition seem to be re- 
presented.^ 

An eyelash which naturally falls, or which can be drawn 



* These and other instances are related more in detail in Mr. Paget's 
Lectures on Surgical Pathology, from which this chapter was originally 
written. 



XUTEITIOX OF HAIE. 



377 



out without pain, is one that has lived its natural time, 
and has died, and been separated from the living parts. 
In its bulb such an one will be found different from those 
that are still living in 
any period of their age. 
In the early period of 
the growth of a dark 
eyelash, the meduUary 
substance appears like 
an interior cylinder of 
darker granular sub- 
stance, continued down 
to the deepest part, 
where the hair enlarges 
to form the bulb. This 
enlargement, which is 
of nearly cup-like form, 
appears to depend on 
the accumulation of 
nucleated cells, whose 
nuclei, according to 
their position, are 
either, by narrowing 

and elongation, to form the fibrous substance of the outer 
part of the growing and further protruding hair, or are to 
be transformed into the granular matter of its medullary 
portion. At the time of early and most active growth, all 
the cells and nuclei contain abundant pigment-matter, and 




* Fig. I02. Intended to represent the changes undergone by a hair 
towards the close of its period of existence. At a, its activity of growth 
is diminishing, as shown by the small quantity of pigment contained in 
the cells of the pulp, and by the interrupted line of dark meduUaiy 
substance. At b, provision is being made for the formation of a new 
hair, by the growth of a new pulp connected with the pulp or capsule 
of the old hair. c. A hair at the end of its period of life, deprived of 
its sheath and of the mass of cells composing the pulp of a living hair. 



378 NUTRITION. 

the whole bulb looks nearly black. The sources of the 
material outof which the cells form themselves are at least 
two ; the inner surface of the sheath or capsule, which 
dips into the skin, enveloping the hair, and the surface of 
a vascular pulp which fits in a conical cavity in the bottom 
of the hair-bulb. 

Such is the state of parts so long as the growing hair is 
all dark. But as the hair approaches the end of its 
existence, instead of the almost sudden enlargement at its 
bulb, it only swells a little, and then tapers nearly to a 
point ; the conical cavity in its base is contracted ; and the 
cells produced on the inner surface of the capsule contain 
no pigment. Still, for some time, it continues thus to live 
and grow ; and the vigour of the pulp lasts rather longer 
than that of the sheath or capsule, for it continues to pro- 
duce pigment-matter for the medullary substance of the 
hair after the cortical substance has become white. Thus 
the column of dark medullary substance appears paler and 
more slender, and perhaps interrupted, down to the point 
of the conical pulp which, though smaller, is still distinct, 
because of the pigment-cells covering its surface. 

At length the pulp can be no longer discerned, and un- 
coloured cells are alone produced, and maintain the latest 
growth of the hair. With these it appears to grow yet 
some further distance ; for traces of the elongation of their 
nuclei into fibres appear in lines running from the inner 
surface of the capsule inwards and along the surface of the 
hair ; and the column of dark medullary substance ceases 
at some distance above the lower end of the contracted 
hair-bulb. The end of all is the complete closure of the 
conical cavity in which the hair-pulp was lodged, the 
cessation of the production of new cells from the inner 
surface of the capsule, and the detachment of the hair 
which, as a dead part, is separated and fallg. 

Such is the life of a hair, and such its death ; which 
death is spontaneous, independent of exercise, or of any 



MAIXTEI^ANCE BY NUTHTTIOX. 



379 



mechanical external force — the natural termination of a 
certain period of life. -Yet, before the hair dies, provision 
is made for its successor : for when its growth is failing, 
there appears below its base a dark spot, the germ or 
young pulp of the new hair covered with cells containing 
pigment, and often connected by a series of pigment cells 
with the old pulp or capsule (fig. 1 02, b). 

Probably there is an intimate analogy between the pro- 
cess of successive life and death, and life communicated to 
a successor, which is here shown, and that which constitutes 
the ordinary nutrition of a part. It may be objected, that 
the death and casting out of the hair cannot be imitated 
in internal parts ; therefore, for an example in which the 
assumed absorption of the worn-out or degenerate internal 
particles is imitated in larger organs at the end of their 
appointed period of life, the instance of the deciduous or 
milk-teeth may be adduced. 

Each milk-tooth is develop- 
ed from its germ ; and in the 
course of its own development, 
separates a portion of itself to 
be the germ of its successor ; 
and each, having reached its 
perfection, retains for a tim 
its perfect state, and stiii 
lives, though it does not grow. 
But at length, as the new tooth 
comes, the deciduous tooth 
dies ; or rather its crown dies, 
and is cast out like the dead hair, while its fang, with 
its bony sheathing, and vascular and nervous pulp, de- 
generates and is absorbed (fig. 103). The degeneration is 



Firj. 103.* 




* Fig. 103. Section of a portion of the uj^per jaw of a child, showing 
a new tooth in process of formation, the fang of the corresponding 
deciduous tooth being absorbed. 



380 NUTRITION. 

accompanied by some unknown spontaneous decomposition 
of the fang; for it could not be absorbed unless it was 
first so changed as to be soluble. And it is degeneration, 
not death, which precedes its removal ; for when a tooth- 
fang dies, as that of the second tooth does in old age, then 
it is not absorbed, but cast out entire, as a dead part. 

Such, or generally such, it seems almost certain, is the 
process of maintenance by nutrition ; the hair and teeth 
may be fairly taken as types of what occurs in other parts, 
for they are parts of €omplex organic structure and com- 
position, and the teeth-pulps, which are absorbed as well 
as the fangs, are very vascular and sensitive. 

Nor are they the only instances that might be adduced. 
The like development, persistence for a time in the perfect 
state, death, and discharge, appear in all the varieties of 
cuticles and gland-cells ; and in the epidermis, as in the 
teeth, there is evidence of decomposition of the old cells, in 
the fact of the different influence which acetic acid and 
potash exercise on them and on the young cells. Seeing, 
then, that the process of nutrition, as thus displayed, both 
in active organs and in elementary cells, appears in these 
respects similar, the general conclusion may be that, in 
nutrition, the ordinary course of each complete elementary 
organ in the body, after the attainment of its perfect state 
by development and growth, is to remain in that state for 
a time ; then, independently of the death or decay of the 
whole body, and, in some measure, independently of its 
own exercise, or exposure to external violence, to die or to 
degenerate ; and then, being cast out or absorbed, to make 
way for its successor. 

It appears, moreover, that the length of life which each 
part is to enjoy is fixed and determinate, though in some 
degree subject to accidents and to the expenditure of life 
in exercise. It is not likely that all parts are made to last 
a certain and equal time, and then all need to be changed. 
The bones, for instance, when once completely formed. 



MAINTENANCE BY NUTRITION. 38 1 

must last longer than the muscles and other softer tissues. 
But when we see that the life of certain parts is of 
determined length, whether they be used or not, we may 
assume, from analogy, the same of nearly all. 

Now, the deciduous human teeth have an appointed 
average duration of life. So have the deciduous teeth of 
all other animals ; and in all the numerous instances of 
moulting, shedding of antlers, of desquamation, change of 
plumage in birds, and of hair in Mammalia, the only ex- 
planation is that these organs have their severally appointed 
times of living, at the ends of which they degenerate, die, 
are cast away, and in due time are replaced by others 
which, in their turn, are to be developed to perfection, to 
live their life in the mature state, and in their turn to be 
cast off. So also, in some elementary structures we may 
discern the same laws of determinate period of life, death, 
or degeneration, and replacement. They are evident in the 
history of the blood-corpuscles, both in the superseding of 
the first set of them by the second at a definite period in 
the life of the embryo, and in the replacement of those 
that degenerate by others new-formed from lymph-cor- 
puscles (see p. 92). And if we could suppose the blood- 
corpuscles grouped together in a tissue instead of floating, 
we might have in the changes they present an image of 
the nutrition of the elements of the tissues. 

The duration of life in each particle is, however, liable to 
be modified ; especially by the exercise of the function of 
the part. The less a part is exercised the longer do its 
component particles appear to live : the more active its 
functions are, the less prolonged is the existence of its 
individual particles. So in the case of single cells ; if the 
general development of the tadpole be retarded by keeping 
it in a cold, dark place, and if hereby the function of the 
blood-corpuscles be slowly and imperfectly discharged, 
they will maintain their embryonic state for even several 
weeks later than usual, the development of the second set 



382 NUTRITION. 

of corpuscles will be proportionally postponed, and the 
individual life of the corpuscles of the first set -wiU be, by 
the same time, prolonged. 

Such being the mode in which the necessity for the pro- 
cess of nutritive maintenance is created, such the sources 
of impairment and waste of the tissues, the next conside- 
ration may be the manner in which the perfect state of a 
part is maintained by the insertion of new particles in the 
place of those that are absorbed or cast off. 

The process by which a new particle is formed in the place 
of the old one is probably always a process of develop- 
ment ; that is, the cell or fibre, or other element of tissue, 
passes in its formation through the same stages of develop- 
ment as those elements of the same tissue did which were 
first formed in the embryo. This is probable from the 
analogy of the hair, the teeth, the epidermis, and all the 
tissues that can be observed : in all, the process of repair 
or replacement is effected through development of the new 
parts. The existence of nuclei or cytoblasts in nearly aU 
parts that are the seats of active nutrition makes the same 
probable. For these nuclei, such as are seen so abundant 
in strong, active muscles, are not remnants of the embryonic 
tissue, but germs or organs of power for new formation, 
and their abundance often appears directly proportionate 
to the activity of growth. Thus, they are always abundant 
in the foetal tissues, and those of the young animal ; and 
they are peculiarly numerous in the muscles and the brain, 
and their disappearance from a part in which they usually 
exist is a sure accompaniment and sign of degeneration. 

A difference may be drawn between what may be called 
nutritive reproduction and nutritive repetition. The former is 
shown in the case of the human teeth. As the deciduous 
tooth is being developed, a part of its productive capsule 
is detached, and serves as a germ for the formation of the 
second tooth ; in which second tooth, therefore, the first 
may be said to be reproduced, in the same sense as that in 



NUTEITIVE EEPKODUCTIOX AND REPETITIOX. 383 

wliich we speak of the organs by which new individuals 
are formed, as the reproductive organs. But in the shark's 
jaws, and others, in which we see row after row of teeth 
succeeding each other, the row behind is not formed of 
germs derived from the row before : the front row is 
simply repeated in the second one, the second in the third, 
and so on. So, in cuticle, the deepest layer of epidermis- 
cells derives no germs from the layer above : their de- 
velopment is not like a reproduction of the cells that 
have gone on towards the surface before them : it is only 
a repetition. It is not improbable that much of the 
difference in the degree of repair, of which the several 
tissues are capable after injuries or diseases, may be con- 
nected with these differences in their ordinary mode of 
nutrition. 

In order that the process of nutrition may be perfectly 
accomplished, certain conditions are necessary. Of these, 
the most important are : i. A right state and composition 
of the blood, from which the materials for nutrition are 
derived. 2. A regular and not far distant supply of such 
blood. 3. A Cvirtain influence of the nervous system. 4. A 
natural state of the part to be nourished. 

I. This right condition of the blood does not necessarily 
imply its accordance with any known standard of com- 
position, common to all kinds of healthy blood, but rather 
the existence of a certain adaptation between the blood 
and the tissues, and even the several portions of each 
tissue. Such an adaptation, peculiar to each individual, is 
determined in its first formation, and is maintained in the 
concurrent development and increase of both blood and 
tissues ; and upon its maintenance in adult life appears to 
depend the continuance of a healthy process of nutrition, 
or, at least, the preservation of that exact sameness of the 
whole body and its parts, which constitutes the perfection 
of nutrition. Some notice of the maintenance of this 
sameness in the blood has been given already (p. 94), in 



384 XUTEITIOX. 

speaking of the po'^er of assimilation which the blood 
exercises, a power exactly comparable with this of main- 
tenance by nutrition in the tissues. And evidence of the 
adaptation between the blood and the tissues, and of the 
exceeding fineness of the adjustment by which it is main- 
tained, is afforded by the phenomena of diseases, in which, 
after the introduction of certain animal poisons, even in 
very minute quantities, the whole mass of the blood is 
altered in composition, and the solid tissues are perverted 
in their nutrition. It is necessary to refer only to such 
diseases as syphilis, small-pox, and . other eruptive fevers, 
in illustration. And when the absolute dependence of all the 
tissues on the blood for their very existence is remembered, 
on the one hand, and, on the other, the rapidity with which 
substances introduced into the blood are diffused into all, 
even non-vascular textures (p. 371), it need be no source of 
wonder that any, even the slightest alteration, from the 
normal constitution of the blood, should be immediately 
reflected, so to speak, as a change in the nutrition of the 
solid tissues and organs which it is destined to nourish. 

2. The necessity of an adequate suj^ijly of appropriate blood 
in or near the part to he nourished, in order that its nutrition 
may be perfect, is shown in the frequent examples of 
atrophy of parts to which too little blood ' is sent, of morti- 
fication or arrested nutrition when the supply of blood is 
entirely cut off, and of defective nutrition when the blood 
is stagnant in a part. That the nutrition of a part may, 
be perfect, it is also necessary that the blood should be 
brought sufficiently near to it for the elements of the tissue 
to imbibe,^ through the walls of the blood-vessels, the 
nutritive materials which they require. The blood-vessels 
themselves take no share in the process of nutrition, except 
as carriers of the nutritive matter. Therefore, provided 
they come so near that this nutritive matter may pass by 
imbibition into the part to be nourished, it is compara- 
tively immaterial whether they ramify within the substance 



CONDITIONS XECESSAEY FOE NUTRITION. 385 

of the tissue, or are distributed only on its surface or 
border. 

The blood-vessels serve alike for the nutrition of the 
vascular and the non-vascular parts, the difference between 
which, in regard to nutrition, is less than it may seem. 
For the vascular, the nutritive fluid is carried in streams 
into the interior ; for the non-vascular, it flows on the sur- 
face ; but in both alike, the parts themselves imbibe the 
fluid ; and although the passage through the walls of the 
blood-vessels may effect some change in the materials, yet 
all the process of formation is, in both alike, outside the 
vessels. Thus, in muscular tissue, the fibrils in the very 
centre of the fibre nourish themselves : yet these are dis- 
tant from all blood-vessels, and can only by imbibition 
receive their nutriment. So, in bones, the spaces between 
the blood-vessels are wider than in muscle ; yet the parts 
in the meshes nourish themselves, imbibing materials from 
the nearest source. The non-vascular epidermis, though 
no vessels pass into its substance, yet imbibes nutritive 
matter from the vessels of the immediately subjacent cutis, 
and maintain^ itself, and grows. The instances of the 
cornea and vitreous humour are stronger, yet similar ; and 
sometimes even the same tissue is in one case vascular, in 
the other not, as the osseous tissue, which, when it is in 
masses or thick layers, has blood-vessels running into it ; 
but when it is in thin layers, as in the lachrymal and tur- 
binated bones, has not. These bones subsist on the blood 
flowing in the minute vessels of the mucous membrane, 
from which the epithelium derives nutriment on one side, 
the bone on the other, and the tissue of the membrane 
itself on every side : a striking instance how, from the 
same source, many tissues maintain themselves, each exer- 
cising its peculiar assimilative and seK-formative power. 

3. The third condition said to be essential to a healthy 
nutrition, is a certain influence of the nervous system. 

It has been held that the nervous system cannot be 

c c 



386 XUTRITIOX. 

essential to a healthy course of nutrition, because in plants 
and the early embryo, and in the lowest animals, in which 
no nervous system is developed, nutrition goes on without 
it. But this is no proof that in animals which have a 
nervous system, nutrition may be independent of it ; 
rather, it may be assumed, that in ascending development, 
as one system after another is added or increased, so the 
highest (and, highest of aU, the nervous system) will 
always be inserted and blended in a more and more inti- 
mate relation with all the rest : according to the general 
law, that the interdependence of parts augments with their 
development. 

The reasonableness of this assumption is proved by many 
facts showing the influence of the nervous system on nutri- 
tion, and by the most striking of these facts being observed 
in the higher animals, and especially in man. The influ- 
ence of the mind in the production, aggravation, and cure 
of organic diseases is matter of daily observation, and a 
sufficient proof of influence exercised on nutrition through 
the nervous system. 

Independently of mental influence, injuries either to 
portions of the nervous centres, or to individual nerves, 
are frequently followed by defective nutrition of the parts 
supplied by the injured nerves, or deriving their nervous 
influence from the damaged portions of the nervous centres. 
Thus, lesions of the spinal cord are sometimes followed by 
mortification of portions of the paralysed jmrts ; and this 
may take place very quickly, as in a case by Sir B. C. 
Brodie, in which the ankle sloughed within twenty-four 
hours after an injury of the spine. After such lesions 
also, the repair of injuries in the paralysed parts may 
take place less completely than in others ; so, Mr. Travers 
mentions a case in which paraplegia was produced by 
fracture of the lumbar vertebrae, and, in the same accident, 
the humerus and tibia were fractured. The former in due 
time united ; the latter did not. The same fact was illus- 



INFLUEXCE OF NERVOtTS SYSTEM. 



387 



trated by some experiments of Dr. Baly, in whicli having, 
in salamanders, cut off the end of the tail, and then thrust 
a thin wire some distance up the spinal canal, so as to de- 
stroy the cord, he found that the end of the tail was repro- 
duced more slowly than in other salamanders in whom the 
spinal cord was left uninjured above the point at which 
the tail was amputated. Illustrations of the same kind 
are furnished by the several cases in which division or 
destruction of the trunk of the trigeminal nerve has been 
followed by incomplete and morbid nutrition of the corre- 
sponding side of the face ; ulceration of the cornea being 
often directly or indirectly one of the consequences of such 
imperfect nutrition. Part of the wasting and slow dege- 
neration of tissue in paralysed limbs is probably referable 
also to the withdrawal of nervous influence from them ; 
though, perhaps, more is due to the want of use of the 
tissues. 

Undue irritation of the trunks of nerves, as well as their 
division or destruction, is sometimes followed by defective 
or morbid nutrition. To this may be referred the cases 
in which ulceration of the parts supplied by the irritated 
nerves occurs frequently, and continues so long as the 
irritation lasts. Further evidence of the influence of the 
nervous system upon nutrition is furnished by those cases 
in which, from mental anguish, or in severe neuralgic head- 
aches, the hair becomes grey very quickly, or even in a few 
hours. 

So many and various facts leave little doubt that the 
nervous system exercises an influence over nutrition as 
over other organic processes ; and they cannot be explained 
by supposing that the changes in the nutritive processes 
are only due to the variations in the size of the blood- 
vessels supplying the affected parts. 

The question remains, through what class of nerves is 
the influence exerted ? When defective nutrition occurs in 
parts rendered inactive by injury of the motor nerve alone, 

c c 2 



2,SS NUTRITION. 

as in the muscles and other tissues of a paratysed face or 
limb, it may appear as if the atrophy were the direct con- 
sequence of the loss of power in the motor nerves ; but it 
is more probable that the atrophy is the consequence of 
the want of exercise of the parts ; for if the muscles be 
exercised by artificial irritation of their nerves their nutri- 
tion will be less defective (J. Reid). The defect of the nutri- 
tive process which ensues in the face and other parts, 
moreover, in consequence of destruction of the trigeminal 
nerve, cannot be referred to loss of influence of any motor 
nerves ; for the motor- nerves of the face and eye, as well as 
the olfactory and optic, have no share in the defective nutri- 
tion which follows injury of the trigeminal nerve; and one 
or all of them may be destroyed without any direct disturb- 
ance of the nutrition of the parts they severally supply. 

It must be concluded, therefore, that the influence which 
is exercised by nerves over the nutrition of parts to which 
they are distributed, is to be referred either to those among 
their branches which conduct impressions to the brain and 
spinal cord, namely, the nerves of common sensation, or, 
as it is by some supposed, by nerve-fibres, which preside 
specially over the nutrition of the tissues and organs 
to which they are supplied. Such special nerves are 
called trophic nerves (see Chapter on the Nervous 
System). 

It is not at present possible to say whether the influence 
on nutrition is exercised through the cerebro-spinal or 
through the sympathetic nerves, which, in the parts on 
which the observation has been made, are generally com- 
bined in the same sheath. The truth perhaps is, that it 
may be exerted through either or both of these nerves. 
The defect of nutrition which ensues after lesion of the 
spinal cord alone, the sympathetic nerves being uninjured, 
and the general atrophy which sometimes occurs in con- 
sequence of diseases of the brain, seem to prove the 
inflaence of the cerebro-spinal system : while the obser- 



INFLUENCE OF NERYOUS SYSTEM. 389 

vation of Magendie and Mayer, that inflammation of the 
eye is a constant result of ligature of the sympathetic 
nerve in the neck, and many other observations of a 
similar kind, exhibit very well the influence of the latter 
nerve in nutrition. 

4. The fourth condition necessary to healthy nutrition is 
a healthy state of the part to be nourished. This seems 
proved by the very nature of the process, which consists in 
the formation of new parts like those already existing; for, 
unless the latter are healthy, the former cannot be so. 
Whatever be the condition of a part, it is apt to be per- 
petuated by assimilating exactly to itself, and endowing 
with all its peculiarities the new particles which it forms 
to replace those that degenerate. So long as a part is 
healthy, and the other conditions of healthy nutrition exist, 
it maintains its healthy condition. But, according to the 
same law, if the structure of a part be diseasied or in any 
way altered from its natural condition, the alteration is 
maintained ; the altered, like the healthy structure, is per- 
petuated. 

The same exactness of the assimilation of the new parts 
to the old, which is seen in the nutrition of the healthy 
tissues, may be observed also in those that are formed in 
disease. By it, the exact form and relative size of a 
cicatrix are preserved from year to year ; by it, the thick- 
ening and induration to which imflammation gives rise are 
kept up, and the various morbid states of the blood in 
struma, syphilis, and other chronic diseases are maintained, 
notwithstanding all diversities of diet. By this precision 
of the assimilating process, may be explained the law that 
certain diseases occur only once in the same person, and 
that certain others are apt to recur frequently ; because in 
both cases alike, the alteration produced by the first attack 
of the disease is maintained by the exact likeness which the 
new parts bear to the old ones. 

The period, however, during which an alteration of 



390 NUTRITION. 

structure may be exactly maintained by nutrition, is not 
unlimited ; for in nearly all altered parts there appears to 
exist a tendency to recover the perfect state ; and, in many 
cases, this state is, in time, attained. To this we may 
attribute the possibility of re-vaccination after the lapse of 
some years ; the occasional recurrence of small-pox, scarlet- 
fever, and the like diseases in the same person ; the wearing 
out of scars, and the complete restoration of tissues that 
have been altered by injury or disease. 

Such are some of the more important conditions which 
appear to be essential to healthy nutrition. Absence or 
defect of any one of them is liable to be followed by dis- 
arrangement of the process ; and the various diseases 
resulting from defective nutrition appear to be due to the 
failure of these conditions, more often than to imperfection 
of the process itself. 

GROWTH. 

Growth, as has been already observed, consists in the 
increase of a part in bulk and weight by the addition to 
its substance of particles similar to its own, but more than 
sufficient to replace those which it loses by the waste or 
natural decay of its tissue. The structure and composi- 
tion of the part remain the same ; but the increase of 
healthy tissue which it receives is attended with the capa- 
bility of discharging a larger amount of its ordinary 
function. 

While development is in progress, growth frequently 
proceeds with it in the same part, as in the formation of 
the various organs and tissues of the embryo, in which 
parts, while they grow larger, are also gradually more 
developed until they attain their perfect state. But, com- 
monly, growth continues after development is completed, 
and in some parts continues even after the full stature 
of the body is attained, and after nearly every portion 



GROWTH. 



391 



of it has gained its perfect state in both size and composi- 
tion. 

In certain conditions, this continuance or a renewal of 
growth may be observed in nearly every part of the body. 
AVhen parts have attained the full size which in the ordi- 
nary process of growth they reach, and are then kept in a 
moderate exercise of their' functions, they commonly (as 
already stated) retain almost exactly the same dimensions 
through the adult period of life. But when, from any cause, 
a part already full-grown in proportion to the rest of the 
body, is called upon to discharge an unusual amount of its 
ordinary function, the demand is met by a corresponding 
increase or growth of the part. Illustrations of this are 
afforded by the increased thickening of cuticle at parts 
where it is subjected to an unusual degree of occasional 
pressure or friction, as in the palms of the hands of persons 
employed in rough manual labour ; by the enlargement 
and increased hardness of muscles that are largely exer- 
cised; and by many other facts of a like kind. The 
increased power of nutrition put forth in such growth is 
greater than might be supposed ; for the immediate effect 
of increased exercise of a part must be a greater using of 
its tissue, and might be expected to entail a permanent 
thinning or diminution of the substance of the part. But 
the energy with which fresh particles are formed is suffi- 
cient not only to replace completely those that are worn 
away, but to cause an increase in the substance of the 
part — the amount of this increase being proportioned to 
the more than usual degree in which its functions are 
exercised. 

The growth of a part from undue exercise of its functions 
is always, in itself, a healthy process ; and the increased 
size which results from it must be distinguished from the 
various kinds of enlargement to which the same part may 
be subject from disease. In the former case the enlarge- 
ment is due to an increased quantity of healthy tissue, 



392 NUTRITIO!n\ 

providing more than the previous power to meet a par- 
ticular emergency ; the other may be the result of a deposit 
of morbid material within the natural structure of the part, 
diminishing, instead of augmenting, its fitness for its office. 
Such a healthy process of growth in a part, attended with 
increased power and activity of its functions, may, however, 
occur as the consequence of disease in some other part ; in 
which case it is commonly called Hypertrophy, i.e., excess 
of nutrition. The most familiar examples of this are in 
the increased thickness and robustness of the muscular 
walla of the cavities of the heart in cases of continued 
obstruction to the circulation ; and in the increased de- 
velopment of the muscular coat of the urinary bladder 
when, from any cause, the free discharge of urine from it 
is interfered with. In both these cases, though the origin 
of the growth is the consequence of disease, yet the growth 
itself is natural, and its end is the benefit of the economy ; 
it is only common growth renewed or exercised in a part 
which had attained its size in due proportion to the rest of 
the body. 

It may be further mentioned, in relation to the phy- 
siology of this subject, that when the increase of function, 
which is requisite in the cases jfrom which hypertrophy 
results, cannot be efficiently discharged by mere increase 
of the ordinary tissue of the part, the development of a 
new and higher kind of tissue is frequently combined with 
this growth. An example of this is furnished by the 
uterus, in the walls of which, when it becomes enlarged 
by pregnancy, or by the growth of fibrous tumours, organic 
muscular fibres, found in a very ill-developed condition in 
its quiescent state, are then enormously developed, and 
provide for the expulsion of the foetus or the foreign body. 
Other examples of the same kind are furnished by cases in 
which, from obstruction to the discharge of their contents 
and a consequently increased necessity for propulsive 
power, the coats of reservoirs and of ducts become the seat 



HYPERTROPHY, 



393 



of development of organic muscular fibres, which could be 
said only just to exist in them before, or were present in a 
very imperfectly develop'ed condition. 

Respecting the mode and conditions of the process of 
growth, it need only be said, that its mode seems to diJffer 
only in degree from that of common maintenance of a part; 
more particles are removed from, and many more added to 
a growing tissue, than to one which only maintains itself. 
But so far as can be ascertained, the mode of removal, the 
disposition of the removed parts, and the insertion of the 
new particles, are as in simple maintenance. 

The conditions also of growth, are the same as those of 
common nutrition, and are equally or more necessary to its 
occurrence. When they are very favourable or in excess, 
growth may occur in the place of common nutrition. Thus 
hair may grow profusely in the neighbourhood of old 
ulcers, in consequence, apparently, of the excessive supply 
of blood to the hair-bulbs and pulps ; bones may increase 
in length when disease brings much blood to them ; and, 
cocks' spurs transplated from their legs into their combs 
grow to an unnatural length ; the conditions common to all 
these cases being both an increased supply of blood, and 
the capability, on the part of the growing tissue, of avail- 
ing itself of the opportunity of increased absorption and 
nutrition thus afforded to it. In the absence of the last- 
named condition, increased supply of blood will not lead 
to increased nutrition. 



394 



CHAPTER XII. 

SECRETION. 



Secretion is the process by which materials are sepa- 
rated from the blood, and from the organs in which they 
are formed, for the purpose either of serving some ulterior 
office in the economy, or being discharged from the body 
as excrement. In the former case, both the separated 
materials and the processes for their separation are termed 
secretions ; in the latter, they are named excretions. 

Most of the secretions consist of substances which, pro- 
bably, do not pre-exist in the same form in the blood, but 
require s;^ecial organs and a process of elaboration for 
their formation, e.g., the liver for the formation of bile, 
the mammary gland for the formation of milk. The ex- 
cretions, on the other hand, commonly or chiefly consist of 
substances which, as urea, carbonic acid, and probably 
uric acid, exist ready-formed in the blood, and are merely 
abstracted therefrom. If from any cause, such as exten- 
sive disease or extirpation of an excretory organ, the sepa- 
ration of an excretion is prevented, and an accumulation 
of it in the blood ensues, it frequently escapes through 
other organs, and may be detected in various fluids of the 
body. But this is never the case with secretions ; at least 
with those that are most elaborated ; for after the removal 
of the special organs by which any of them is elaborated, 
it is no longer formed. Cases sometimes occur in which 
the secretion continues to be formed by the natural organ, 
but not being able to escape towards the exterior, on ac- 
count of some obstruction, is re-absorbed into the blood, 
and afterwards discharged from it by exudation in other 
ways ; but these are not instances of true vicarious secre- 
tion, and must not be thus regarded. 

These circumstances, and their final destination, are, 



SEROUS MEMBRANES. 395 

however, the only particulars in which secretions and 
excretions can be distinguished ; for, in general, the struc- 
ture of the parts engaged in eliminating excretions, e.g.j 
the kidneys, is as complex, as that of the parts concerned 
in the formation of secretions. And since the differences 
of the two processes of separation, corresponding with 
those in the several purposes and destinations of the fluids, 
are not yet ascertained, it will be sufficient to speak in 
general terms of the process of separation or secretion. 

Every secreting apparatus possesses, as essential parts 
of its structure, a simple and apparently textureless mem- 
brane, named the primary or basement-membrane ; certain 
cells; and blood-vessels. These three structural elements 
are arranged together in various w^ays ; but all the varieties 
may be classed under one or other of two principal divi- 
sions, namely, membranes and glands. 

SECRETING MEMBRANES. 

The principal secreting membranes are the serous and 
synovial membranes, the mucous membranes, and the 
skin.* 

Fig. I04.t 

.& 



The serous membranes are formed of fibro-cellular tissue, 
interwoven so as to constitute a membrane, the free surface 
of which is covered with a single layer of flattened cells, 
forming, in most instances, a simple tesselated epithelium. 
Between the epithelium and the subjacent layer of fibro- 
cellular tissue, is situated the primary or basement mem- 
brane (Bowman). 

* The skin will be described in a subseciuent chapter. 

t Fig. 104. Plan of a secreting membrane : a, memhrana propria, or 
basement-membrane ; h, epithelium composed of secreting nucleated 
cells ; c, layer of capillary blood-vessels (after Sharpey). 



396 SECEETIOX. 

In relation to the process of secretion, the layer of fibro- 
cellular tissues serves as a ground- work for the ramification 
of blood-vessels, lymphatics, and nerves. But in its usual 
form it is absent in some instances, as in the arachnoid 
covering the dura mater, and in the interior of the ven- 
tricles of the brain. The primary membrane and epithe- 
lium are probably always present, and are concerned in 
the formation of the fluid by which the free surface of the 
membrane is moistened. 

The serous membranes are of two principal kinds : 
1st. Those which line visceral cavities, — the arachnoid, 
pericardium, pleurae, peritoneum, and tunicse vaginales. 
27id. The synovial membranes lining the joints, and the 
sheaths of tendons and ligaments, with which, also, are 
usually included the s}Tiovial bursae, or bursa mucoscB, 
whether these be subcutaneous, or situated beneath ten- 
dons that glide over bones. 

The serous membranes form closed sacs, and exist 
wherever the free surfaces of viscera come into contact 
with each other, or lie in cavities unattached to surround- 
ing parts. The viscera, which are invested by a serous 
membrane, are, as it were, pressed into the shut sac which 
it forms, carrying before them a portion of the membrane, 
which serves as their investment. To the law that serous 
membranes form shut sacs, there is, in the human subject, 
one exception, viz. : the opening of the Fallopian tubes 
into the abdominal cavity, — an arrangement which exists 
in man and all Vertebrata, with the exception of a few 
fishes. 

The principal purpose of the serous and synovial mem- 
branes is to furnish a smooth, moist surface, to facilitate 
the movements of the invested organ, and to prevent the 
injurious effects of friction. This purpose is especially 
manifested in joints, in which free and extensive move- 
ments take place ; and in the stomach and intestines, which, 
from the varying quantity and movements of their contents, 



SEEOUS MEMBRANES. 39;^ 

are in almost constant motion upon one another and the 
walls of the abdomen. 

The fluid secreted from the free surface of the serous mem- 
branes is, in health, rarely more than sufficient to ensure the 
maintenance of their moisture. The opposed surfaces of each 
serous sac, are at every point in contact with each other, and 
leave no space in which fluid can collect. After death, a larger 
quantity of fluid is usually found in each serous sac; but this, 
if not the product of manifest disease, is probably such as has 
transuded after death, or in the last hours of life. An excess of 
such fluid in any of the serous sacs constitutes dropsy of the sac. 

The fluid naturally secreted by the serous membranes 
appears to be identical, in general and chemical characters, 
with the serum of the blood, or with very dilute liquor san- 
guinis. It is of a pale yellow or straw-colour, slightly 
viscid, alkaline, and, because of the presence of albumen, 
coagulable by heat. The presence of a minute quantity 
of fibrin, at least in the dropsical fluids effused into the 
serous cavities, is shown by their partial coagulation into a 
jelly-like mass, on the addition of certain animal substances, 
or on mixture with certain fluids, especially such as contain 
cells (p. 75 et seq.). This similarity of the serous fluid to 
the liquid part of blood, and to the fluid with which most 
animal tissues are moistened, renders it probable that it 
is, in great measure, separated by simple transudation 
through the walls of the blood-vessels. The probability 
is increased by the fact that, in jaundice, the fluid in the 
serous sacs is, equally with the serum of the blood, coloured 
with the bile. But there is reason for supposing that the 
fluid of the cerebral ventricles and of the arachnoid sac 
are exceptions to this rule ; for they differ from the fluids 
of the other serous sacs not only in being pellucid, colour- 
less, and of much less specific gravity, but in that they 
seldom receive the tinge of bile in the blood, and are not 
coloured by madder, or other similar substances introduced 
abundantly into the blood. 



398 SECRETION. 

It is also probable that the formation of synovial fluid 
is a process of more genuine and elaborate secretion, by- 
means of the epithelial cells on the surface of the mem- 
brane, and especially of those which are accumulated on 
the edges and processes of the synovial fringes ; for, in its 
peculiar density, viscidity, and abundance of albumen, 
synovia differs alike from the serum of blood and from 
the fluid of any of the serous cavities. 

The mucous membranes line all those passages by which 
internal parts communicate with the exterior, and by 
which either matters are eliminated from the body or 
foreign substances taken into it. They are soft and 
velvety, and extremely vascular. Their general structure 
resembles that of serous membranes. It consists of 
epithelium, basement membrane, and fibro- cellular or 
areolar tissue containing blood-vessels, lymphatics, and 
nerves. The structure of mucous membranes is less 
uniform, . especially as regards their epithelium, than that 
of serous membranes ; but the varieties of structure 
in different parts are described in connection with 
the organs in which mucous membranes are present, 
and need not be here noticed in detail. The external 
surfaces of mucous membranes are attached to various 
other tissues ; in the tongue, for example, to muscle ; 
on cartilaginous parts, to perichondrium ; in the ceUs of 
the ethmoid bone, in the frontal and sphenoid sinuses, 
as well as in the tympanum, to periosteum ; in the 
intestinal canal, it is connected with a firm submucous 
membrane, which on its exterior gives attachment to the 
fibres of the muscular coat. 

The mucous membranes are described as lining certain 
principal tracts. I . The digestive tract commences in the 
cavity of the mouth, from which prolongations pass into 
the ducts of the salivary glands. From the mouth it passes 
through the fauces, pharynx, and oesophagus, to the 
stomach, and is thence continued along the whole tract of 



MUCOUS MEMBRANES. 399 

the intestinal canal, to the temiination of the rectum, being 
in its course arranged in the various folds and depressions 
already described, and prolonged .into the ducts of the 
pancreas and liver and into the gall-bladder. 2. The 
respiratory tract includes the mucous membrane lining the 
cavity of the nose, and the various sinuses communicating 
with it, the lachrymal canal and sac, the conjunctiva of the 
eye and eyelids, and the prolongation which passes along 
the Eustachian tubes and lines the tympanum and the 
inner surface of the membrana tympani. Crossing the 
phaiynx, and lining that part of it which is above the soft 
palate, the respiratory tract leads into the glottis, whence 
it is continued, through the larynx and trachea, to the 
bronchi and their divisions, which it lines as far as the 
branches of about .,V of an inch in diameter, and con- 
tinuous with it is a layer of delicate epithelial mem- 
brane which extends into the pulmonary cells. 3. The 
(jenito-urinary tract, which lines the whole of the urinary 
passages, from their external orifice to the termination 
of the tubuli uriniferi of the kidneys, extends into and 
through the oigans of generation in both sexes, into the 
ducts of the glands connected with them; and in the female 
becomes continuous with the serous membrane of the abdo- 
men at the fimbriae of the Fallopian tubes. 

Along each of the above tracts, and in different portions 
of each of them, the mucous membrane presents certain 
structural peculiarities adapted to the functions which each 
part has to discharge; yet in some essential characters 
mucous membrane is the same, from whatever part it is 
obtained. In all the principal and larger parts of the several 
tracts, it presents, as just remarked, an external layer of 
epithelium, situated upon basement-membrane, and beneath 
this, a stratum of vascular tissue of variable thickness, 
which in different cases presents either out-growths in the 
form of papillae and villi, or depressions or involutions in the 
form of glands. But in the prolongations of the tracts, where 



400 SECEETIOX. 

they pass into gland-ducts, these constituents are reduced 
in the finest branches of the ducts to the epithelium, the 
primary or basement-membrane, and the capillary blood- 
vessels spread over the outer surface of the latter in a 
single layer. 

The primary or basement-membrane is a thin trans- 
parent layer, simple, homogeneous, and with no discernible 
structure, which, on the larger mucous membranes that 
have a layer of vascular fibro-cellular tissue, may appear 
to be only the blastema or formative substance, out of 
which successive layers of epithelium-cells are formed. 
But in the minuter divisions of the mucous membranes, 
and in the ducts of glands, it is the layer continous and 
correspondent with this basement-membrane that forms 
the proper walls of the tubes. The cells also which, lining 
the larger and coarser mucous membranes, constitute their 
epithelium, are continuous with, and often similar to 
those which, lining the gland-ducts, are called gland-cells, 
rather than epithelium. Indeed, no certain distinction 
can be drawn between the epithelium- cells of mucous 
membranes and gland-cells. In reference to their position, 
as covering surfaces, they might all be called epithelium - 
cells, whether they lie on open mucous membranes, or in 
gland-ducts ; and in reference to the process of secretion, 
they might all be called gland-cells, or at least secreting- 
cells, since they probably all fulfil a secretory office by 
separating certain definite materials from the blood and 
from the part on which they are seated. It is only an 
artificial distinction which makes them epithelial cells in 
one place, and gland-cells in another. 

It thus appears, that the tissues essential to the pro- 
duction of a secretion are, in their simplest form, a simple 
membrane, having on one surface blood-vessels, and on 
the other a layer of cells, which may be called either 
epithelium-cells or gland-cells. Glands are provided also 
with lymphatic vessels and nerves. The distribution of 



SECRETIXG GLANDS. 401 

the former is not peculiar, and need not be here con- 
sidered. Nerve-fibres are distributed both to the blood- 
vessels of the gland and to its ducts ; and, in some glands, 
it is said, to the secreting cells also. 

The structure of the elementary portions of a secreting 
apparatus, namely epithelium, simple membrane, and 
blood-vessels, having been already described in this and 
previous chapters, we may proceed to consider the manner 
in which they are arranged to form the varieties of 
secreting glands. 

SECRETING GLANDS. 

The secreting glands are the organs to which the office 
of secreting is more especially ascribed : for they appear to 
be occupied with it alone. They present, amid manifold 
diversities of form and composition, a general plan of 
structure, by which they are distinguished from all other 
textures of the body ; especially, all contain, and appear 
constructed with particular regard to the arrangement of, 
the cells, which, as already expressed, both line their tubes 
or cavities as zlu epithelium, and elaborate, as secreting 
cells, the substances to be discharged from them. 

For convenience of description, they may be divided into 
three principal groups, the characters of each of which are 
determined by the different modes in which the sacculi or 
tubes containing the secreting cells are grouped : — 

I. The simple tubule, or tubular gland (a, fig. 105), exam- 
ples of which are furnished by the several tubular follicles 
in mucous membranes : especially by the follicles of Lie- 
berkiihn in the mucous membrane of the intestinal canal 
(p. 300), and the tubular or gastric glands of the stomach 
(p. 268). These appear to be simple tubular depressions of 
the mucous membrane on which they open, each consisting 
of an elongated gland- vesicle, the wall of which is formed 
of primary membrane, and is lined with secreting cells 
arranged as an epithelium. To the same class may be 

D D 



402 



SECRETION. 



referred the elongated and tortuous sudoriparous glands of 
the skin (p. 426), and the Meibomian follicles beneath the 
palpebral conjectiva; though the latter are made more 




* Fig. 105. Plans of extension of secreting membrane by inversion or 
recession in form of cavities. A, simple glands, viz., g, straight tube ; 
h, sac ; *', coiled tube. B, multilocular crypts ; Tc, of tubular form : 
I, saccular. C, racemose, or saccular compound gland ; m, entire 
gland, showing branched duct and lobular structure ; n, a lobule, de- 
tached with 0, branch of duct proceeding from it. D, compound 
tubular gland (after Sharpey). 



SECRETING GLANDS. 



403 



complex by the presence of small pouches along their sides 
(b, fig. 105), and form a connecting link between the 
members of this division and the next, as the former by 
their length and tortuosity do between the first division 
and the third (d, fig. 105). 

2. The aggregated glands, including those that used to be 
called conglomerate, in which a number of vesicles or acini are 
arranged in groups or lobules (c, fig. 105) • Such are all those 
commonly called mucous glands, as those of the trachea, 
vagina, and the minute salivary glands. Such, also, are 
the lachrymal, the large salivary and mammary glands, 
Brunn's, Cowper's, and Duverney's glands, the pancreas 
and prostate. These various organs differ from each other 
only in secondary points of structure ; such as, chiefly, the 
arrangement of their excretory ducts, the grouping of the 
acini and lobules, their connection by fibro-cellular tissue, 
and supply of blood-vessels. The acini commonly appear 
to be formed by a kind of fusion of the walls of several 
vesicles, which thus combine to form one cavity lined or 
filled with secreting cells which also occupy recesses from 
the main cavity. The smallest branches of the gland-ducts 
sometimes open into the centres of these cavities ; some- 
times the acini are clustered round the extremities, or by 
the sides of the ducts : but, whatever secondary arrange- 
ment there may be, all have the same essential character 
of rounded groups of vesicles containing gland-cells, and 
opening, either occasionally or permanently, by a common 
central cavity into minute ducts, which ducts in the large 
glands converge and unite to form larger and larger 
branches, and at length, by one common trunk, open on a 
free surface of membrane. " •' 

3. The convoluted tubular glands (d. fig. 105), such as the 
kidney and testis, form another division. These consist of 
tubules of membrane, lined with secreting cells arranged 
like an epithelium. Through nearly the whole of their 
long course, the tubules present an almost uniform size and 

D D 2 



404 SECEETIOX. 

structure ; ultimately they terminate either in a cul-de-sac, 
or by dilating, as in the Malpighian capsules of the kidnej-, 
or by forming a simple loop and returning, as in the 
testicle. 

Among these varieties of structure, all the permanent 
glands are alike in some essential points, besides those 
which they have in common with all truly secreting struc- 
tures. They agree in presenting a large extent of secreting 
surface within a comparatively small space ; in the circum- 
stance that while one end of the gland-duct opens on a 
free surface, the opposite end is always closed, having 
no direct communication with blood-vessels, or any other 
canal ; and in an uniform arrangement of capillary blood- 
vessels, ramifying and forming a network around the walls 
and in the interstices of the ducts and acini. 

PBOCESS OF SECKETION. 

From what has been said, it will have already appeared 
that the modes in which secretions are produced are at least 
two. Some fluids, such as the secretions of serous mem- 
branes, appear to be simply exudations or oozings from the 
blood-vessels, whose qualities are determined by those of 
the liquor sanguinis, while the quantities are liable to 
variation, or are chiefly dependent on the pressure of the 
blood on the interior of the blood-vessels. But, in the 
production of the other secretions, such as those of mucous 
membranes and all glands, other besides these mechanical 
forces are in operation. Most of the secretions are indeed 
liable to be modified by the circumstances which afiect 
the simple exudation from the blood-vessels, and the pro- 
ducts of such exudations, when excessive, are apt to be 
mixed with the more proper products of all the secreting 
organs. But the act of secretion in all glands is the result 
of the vital processes of cells or nuclei, which, as they 
develop themselves and grow, form in their interior the 



DISCHARGE OF SECEETIOXS. 405 

proper materials of tlie secretion, and then discharge 
them. 

The best evidence for this view is : ist. That cells and 
nuclei are constituents of all glands, however diverse their 
outer forms and other characters, and are in all glands 
placed on the surface or in the cavity whence the secretion 
is poured. 27id. That many secretions which are visible 
with the microscope may be seen in the cells of their 
glands before they are discharged. Thus, bile may be 
often discerned by its yellow tinge in the gland-cells of the 
liver; spermatozoids in the cells of the tubules of the 
testicles ; granules of uric acid in those of the kidneys of 
fish ; fatty particles, like those of milk, in the cells of the 
mammary gland. 

The process of secretion might, therefore, be said to be 
accomplished in, and by the life of, these gland-cells. 
They appear, like the cells or other elements of any other 
organ, to develop themselves, grow, and attain their indi- 
vidual perfection by appropriating the nutriment from the 
adjacent blood-vessels, and elaborating into the materials 
of their walls and the contents of their cavities. In this 
perfected state, they subsist for some brief time, and when 
that period is over they appear to dissolve or burst and 
yield themselves and their contents to the peculiar material 
of the secretion. And this appears to be the case in every 
part of the gland that contains the appropriate gland-cells ; 
therefore not in the extremities of the ducts or in the acini 
alone, but in great part of their length. 

In these things there is the closest resemblance between 
secretion and nutrition; for, if the purpose which the 
secreting glands are to serve in the economy be disre- 
garded, their formation might be considered as only the 
process of nutrition of organs, whose size and other con- 
ditions are maintained in, and by means of, the continual 
succession of cells developing themselves and passing 
away. In other words, glands are maintained by the 



4o6 SECRETION. 

development of the cells, and their continuance in the 
perfect state: and the secretions are discharged as the 
constituent gland-cells degenerate and are set free. The 
processes of nutrition and secretion are similar, also, in 
their obscurity : there is the same difficulty in saying why, 
out of apparently the same materials, the cells of one gland 
elaborate the components of bile, while those of another 
form the components of milk, and of a third those of saliva, 
as there is in determining why one tissue forms cartilage, 
another bone, a third muscle, or any other tissue. In 
nutrition, also, as in secretion, some elements of tissues, 
such as the gelatinous tissues, are different in their 
chemical properties from any of the constituents ready- 
formed in the blood. Of these differences, also, no 
account can be rendered ; but, obscure as the cause of 
these diversities may be, they are not objections to the 
explanation of secretion as a process similar to nutrition ; 
an explanation with which all the facts of the case are 
reconcilable. 

It may be observed that the diversities presented by the 
other constituents of glands afford no explanation of the 
differences or peculiarities of their several products. There 
are many differences in the arrangements of the blood- 
vessels in different glands and mucous membranes ; and, 
in accordance with these, much diversity in the rapidity 
with which the blood traverses them. But there is no 
reason for believing that these things do more than in- 
fluence the rate of the process and the quantity of the 
material secreted. Ceteris paribus, the greater the vascu- 
larity of a secreting organ, and the larger the supply of 
blood traversing its vessels in a given time, the larger is 
the amount of secretion ; but there is no evidence that the 
quantity or mode of movement of the blood can directly 
determine the quality of the secretion. 

The Discharge of Secretions from glands may take place 
as soon as they are formed ; or the secretion may be long 



DISCHAEGE OF SECRETIONS. 407 

retained within the gland or its ducts. The secretions of 
glands which are continually in active function for the 
purification of the blood, such as the kidneys, are generally 
discharged from the gland as rapidly as they are formed. 
But the secretions of those whose activity of function is 
only occasional, such as the testicle, are usually retained 
in the ducts during the periods of the gland's inaction. 
And there are glands which are like both these classes, 
such as the lachrymal and salivary, which constantly 
secrete small portions of fluid, and on occasions of greater 
excitement discharge it more abundantly 

When discharged into the ducts, the further course of 
secretions is effected partly by the pressure from behind ; 
the fresh quantities of secretion propelling those that were 
formed before. In the larger ducts, its propulsion is 
assisted by the contraction of their walls. All the larger 
ducts, such as the ureter and common bile-duct, possess in 
their coats organic muscular fibres ; they contract when 
irritated, and sometimes manifest peristaltic movements. 
Bernard and Brown- Sequard, indeed, have observed rhyth- 
mic contractions in the pancreatic and bile-ducts, and 
also in the ureters and vasa deferentia. It is probable 
that the contractile power extends along the ducts to a 
considerable distance within the substance of the glands 
whose secretions can be rapidly expelled. Saliva and 
milk, for instance, are sometimes ejected with much force ; 
doubtless by the energetic and simultaneous contraction of 
many of the ducts of their respective glands. The contrac- 
tion of the ducts can only expel the fluid they contain 
through their main trunk ; for at their opposite ends all 
the ducts are closed. 

Circumstances infiuencing Secretion. — The influence of 
external conditions on the functions of glands, is mani- 
fested chiefly in alterations of the quantity of secretion ; 
and among the principal of these conditions are variations 
in the quantity of blood, in the quantity of the peculiar 



408 SECEETIOX. 

materials for any secretion that it may contain, and in the 
conditions of the nerves of the glands. 

In general, an increase in the quantity of blood traversing 
a gland, coincides with an augmentation of its secretion. 
Thus, the mucous membrane of the stomach becomes florid 
when, on the introduction of food, its glands begin to 
secrete : the mammary gland becomes much more vascular 
during lactation ; and it appears that all circumstances 
which give rise to an increase in the quantity of material 
secreted by an organ, produced, coincidently, an increased 
supply of blood. In most cases, the increased supply of 
blood rather follows than precedes the increase of secre- 
tion ; as, in the nutritive processes, the increased nutrition 
of a part just precedes and determines the increased 
supply of blood ; but, as also in the nutritive process, an 
increased supply of blood may have, for a consequence, an 
increased secretion from the glands to which it is sent. 

Glands also secrete with increased activity when the 
blood contains more than usual of the materials they are 
designed to separate. Thus, when an excess of urea is 
in the blood, whether from excessive exercise, or from 
destruction of one kidney, a healthy kidney will excrete 
more than it did before. It will, at the same time, grow 
larger : an interesting fact, as proving both that secretion 
and nutrition in glands are identical, and that the presence 
of certain materials in the blood may lead to the formation 
of structures in which they may be incorporated. 

The process of secretion is, also, largely influenced by 
the condition of the nervous system. 

The exact mode in which the nervous system influences 
secretion must be still regarded as somewhat obscure. In 
part, it exerts its influence by increasing or diminishing the 
quantity of blood supplied to the secreting gland, in virtue 
of the power which it exercises over the contractility of the 
smaller blood-vessels ; while it also has a more direct in- 
fluence analogous to the trophic influence referred to in the 



INFLUENCE OF NERVOUS SYSTEM. 



409 



chapter on Nutkitiois'. Its influence over secretion, as well 
as over other functions of the body, may be excited by 
causes acting directly upon the nervous centres, upon the 
nerves going to the secreting organ, or upon the nerves of 
other parts. In the latter case, a reflex action is produced : 
thus the impression produced upon the nervous centres by 
the contact of food in the mouth, is reflected upon the 
nerves supplying the salivary glands, and produces, through 
these, a more abundant secretion of saliva. 

Through the nerves, various conditions of the mind also 
influence the secretions. Thus, the thought of food may 
be suflicient to excite an abundant flow of saliva. And, 
probably, it is the mental state which excites the abundant 
secretion of urine in hysterical paroxysms, as weU as the 
perspirations and, occasionally, diarrhoea, which ensue under 
the influence of terror, and the tears excited by sorrow or 
excess of joy. The quality of a secretion may also be 
affected by the mind ; as in the cases in which, through 
grief or passion, the secretion of milk is altered, and is ^ 
sometimes so changed as to produce irritation in the 
alimentary canal of the child, or even death (Carpenter.) 

The secretions of some of the glands seem to bear a 
certain relation or antagonism to each other, by which an 
increased activity of one is usually followed by diminished 
activity of one or more of the others; and a deranged 
condition of one is apt to entail a disordered state in the 
others. Such relations appear to exist among the various 
mucous membranes : and the close relation between the 
secretion of the kidney and that of the skin is a subject of 
constant observation. 



410 



CHAPTER XIII. 

THE VASCULAR GLANDS; OR GLANDS WITHOUT DUCTS. 

The materials separated from the blood by the ordinary- 
process of secretion by glands, are always discharged from 
the organ in which they are formed, and either straight- 
way expelled from the body, or if they are again received 
into the blood, it is only after they have been altered from 
their original condition, as in the cases of the saliva and 
bile. There appears, however, to be a modification of the 
process of secretion, in which certain materials are ab- 
stracted from the blood, undergo some change, and are 
added to the lymph or restored to the blood, without being 
previously discharged from the secreting organ, or made 
use of for any secondary purpose. The bodies in which 
this modified form of secretion takes place, are usually 
described as vascular glands, or glands without ducts, and 
include the spleen, the thymus and thyroid glands, the 
supra-renal capsules, and, according to (Esterlin and 
Ecker and Gull, the pineal gland and pituitary body; 
possibly, also the tonsils. 

The solitary and agminate glands of the intestine 
(p. 302), and lymph-glands in general also closely resem- 
ble them; indeed, both in structure and function, the 
vascular glands bear a close relation, on the one hand, 
to the true secreting glands, and on the other, to the 
Ijonphatlc glands. 

The evidence in favour of the view that these organs 
exercise a function analogous to that of secreting glands, 
has been chiefly obtained from investigations into their 
structure, which have shown that most of the glands with- 
out ducts contain the same essential structures as the 
secreting glands, except the ducts. They are mainly com- 



1 



THE DUCTLESS GLANDS. 411 

posed of vesicles, or sacculi, either simple and closed, as in 
the thyroid (fig. 106), and supra-renal capsules, or 
variously branched, and with the cavities of the several 
branches communicating in and by common canals, as in 
the thymus (fig. 107). These vesicles, like the acini of 
secreting glands, are formed of a delicate homogeneous 
membrane, are surrounded with and often traversed by a 
vascular plexus, and are filled with finely molecular albu- 
minous fluid, suspended in which are either granules of 

FUi. 106.* 




fat, or cytoblasts or nuclei, or nucleated cells, or a mixture 
of all these. 

Structure of the Sj^leen. — The spleen is covered exter- 
nally almost completely by a serous coat derived from the 
peritoneum, while within this is the proper fibrous coat or 
capsule of the organ. The latter, composed of connec- 
tive tissue, with a large preponderance of elastic fibres, 
forms the immediate investment of the spleen. Prolonged 
from its inner surface are fibrous processes or traheculcB, 

* Fig. 106. Vesicles from the Thyroid Gland of a Child (from Kbl- 
liker) ~'^' cc, connective tissue between the vesicles ; b, capsule of the 
vesicles ; c, their epithelial lining. 



412 



THE DUCTLESS GLAXDS. 



whicli enter tlie interior of the organ, and, dividing and 
anastomosing in all parts, form a kind of supporting 
framework or stroma, in the interstices of which the 
proper substance of the spleen, or the spleen-pulp, is con- 
tained. At the hilus of the spleen, or the part at which 
the blood-vessels, nerves, and lymphatics enter, the fibrous 

coat is prolonged into the 
spleen-substance in the form 
of investing sheaths for the 
arteries and veins, which 
sheaths again are connected 
with the trahecidcB before re- 
ferred to. 

The spleen-pulp, which is 
a dark-red or reddish-brown 
colour, is composed chiefly 
of cells. Of these, some are 
granular corpuscles resem- 
bling the lymph- corpuscles, 
both in general appearance 
and in being able to perform 
amoeboid movements ; others 
are red blood-corpuscles of 
normal appearance or variously changed; while there are also 
large cells containing either pigment allied to the colouring 
matter of the blood, or rounded corpuscles like red blood-cells. 
The splenic artery which enters the spleen by its con- 
cave surface or hilus divides and subdivides, with but 
little anastomosis between its branches, in the midst of the 
spleen-pulp, at the same time that its branches are 




* Fig. 107. Transverse Section of a Lobule of an Injected Infantile 
Thymus Gland (after Kolliker) (magnified 30 diameters), a, capsule 
of connective tissue surrounding tlie lobule ; b, membrane of the 
glandular vesicles ; c, cavity of the lobule, from which the larger blood- 
vessels are seen to extend towards and ramify in the spheroidal masses 
of the lobule. 



STRUCTURE OF THE SPLEEN. 413 

slieathed, as before said, by the fibrous coat, whicli they, 
so to speak, carry into the spleen with them. Ending in 
capillaries, they either communicate, as in other parts of 
the body, with the radicles of the veins, or end in lacunar 
spaces in the spleen-pulp, from which veins arise (Gray). 
On the face of a section of the spleen can be usually 

Fly. 108.* 




seen, readily with the naked eye, minute, scattered, rounded 
or oval whitish spots, mostly from -jV to -^^ inch in dia- 
meter. These are the Malpighian coi-puscles of the spleen, 
and are situated on the sheaths of the minute splenic 
arteries, of which, indeed, they may be said to be out- 
growths (fig. 108). For while the sheaths of the larger 
arteries are constructed of ordinary connective tissue, this 
has become modified where it forms an investment for the 



* Fig. 108. The figure shows a. portion of a small artery, to one of the 
twigs of which the Malpighian corpuscles are attached. 



414 



THE DUCTLESS GLANDS. 



smaller vessels, so as to be a fine retiform tissue, with 
abundance of corpuscles, like lymph- corpuscles contained 
in its meshes ; and the Malpighian corpuscles are but 
small outgrowths of this cytogenous or cell-bearing con- 
nective tissue. They are composed of masses of corpuscles, 
intersected in all parts by a delicate fibrillar tissue, which, 
though it invests the ^Malpighian bodies, does not form a 
complete capsule. Blood-capillaries traverse the Malpi- 
ghian corpuscles and form a plexus in their interior. The 
structure of a Malpighian corpuscle of the spleen is, 
therefore, very similar to that of lymphatic-gland sub- 
stance (p. 355)- 



The general resemblances in structure between certain of 
the vascular glands and the true glands lead to the supposi- 
tion that both sets of organs pursue, up to a certain point, 
a similar course in the discharge of their functions. It 
is assumed that certain principles in an inferior state of 
organization are effused from the vessels into the sacculi, 
and gradually develop into nuclei or cytoblasts, which may 
be further developed into cells ; that in the growth of these 
nuclei and cells, the materials derived from the blood are 
elaborated into a higher condition of organization; and 
that when liberated by the dissolution of these cells, they 
pass into the lymphatics, or are again received into the 
blood, whose aptness for nutrition they contribute to 
maintain. 

The opinion that the vascular glands thus^serve for the 
higher organization of the blood, is supported by their 
being all especially active in the discharge of their functions 
during foetal life and childhood, when, for the development 
and growth of the body, the most abundant supply of 
highly organized blood is necessary. The bulk of the 
thymus gland, in proportion to that of the body, appears to 
bear almost a direct proportion to the activity of the body's 



FUNCTIONS OF DUCTLESS GLANDS. 415 

development and growth, and when, at the period of 
puberty, the development of the body may be said to be 
complete, the gland wastes, and finally disappears. The 
thyroid gland and supra-renal capsules, also, though they 
probably never cease to discharge some amount of function, 
yet are proportionally much smaller in childhood than in 
foetal life and infancy ; and with the years advancing to 
the adult period, they diminish yet more in proportionate 
size and apparent activity of function. The spleen more 
nearly retains its proportionate size, and enlarges nearly as 
the whole body does. 

The function of the vascular glands seems not essential 
to life, at least not in the adult. The thymus wastes and 
disappears ; no signs of illness attend some of the diseases 
which wholly destroy the structure of the thyroid gland ; 
and the spleen has been often removed ia animals, and in 
a few instances in men, without any evident ill-consequence. 
It is possible that, in such cases, some compensation for 
the loss of one of the organs may be afforded by an in- 
creased activity of function in those that remain. The 
experiment, to be complete, should include the removal of 
all these organs, an operation of course not possible without 
immediate danger to life. Nor, indeed, would this be 
certainly sufficient, since there is reason to suppose that the 
duties of the spleen, after its removal, might be performed 
by lymphatic glands, between whose structure and that of 
the vascular glands there is much resemblance, and which, 
it is said, have been found peculiarly enlarged when the 
spleen has been removed (Meyer). 

Although the functions of all the vascular glands may 
be similar, in so far as they may all alike serve for the 
elaboration and maintenance of the blood, yet each of them 
probably discharges a peculiar office, in relation either to 
the whole economy, or to that of some other organ. 
Respecting the special office of the thyroid gland, nothing 
reasonable can be suggested ; nor is there any certain 



41 6 THE DUCTLESS GLANDS. 

evidence concerning that of the supra-renal capsules.* 
Respecting the thymus gland, the observations of Mr. 
Simon, confirmed by those of Friedleben, and others, have 
shown that in the hybernating animals, in which it exists 
throughout life, as each successive period of hybernation 
approaches, the thymus greatly enlarges and becomes laden 
with fat, which accumulates in it and in fat-glands connected 
with it, in even larger proportions than it does in the 
ordinary seats of adipose tissue. Hence it appears to serve 
for the storing up of materials which, being re-absorbed in 
inactivity of the hybernating period, may maintain the 
respiration and the temperature of the body in the reduced 
state to which they fall during that time. 

With respect to the office of the spleen, we have 
somewhat more definite information. In the first place, 
the large size which it gradually acquires towards the ter- 
mination of the digestive process, and the great increase 
observed about this period in the amount of the finely- 
granular albuminous plasma within its parenchyma, and 
the subsequent gradual decrease of this material, seem to 
indicate that this organ is concerned in elaborating the 
albuminous or formative materials of food, and for a time 
storing them up, to be gradually introduced into the blood, 
according to the demands of the general system. The 
small amount of fatty matter in such plasma, leads to the 
inference that the gland has little to do in regard to the 
preparation of material for the respiratory process. 



* Mr. J. Hutchinson, and, more recently, Dr. "VVilks, following out 
Dr. Addison's discovery, have, by the collection of a large and valuable 
series of cases in which the supra-renal capsules were diseased, demon- 
strated most satisfactorily the very close relation subsisting between 
disease of these organs and brown discoloration of the skin ; but the 
explanation of this relation is still involved in obscurity, and conse- 
quently does not aid much in determining the functions of the supra- 
renal capsules. 



FUNCTIO^^S OF SPLEEX. 417 

Then again, it seems not improbable tbat, as Hewson 
originally suggested, the spleen, and perhaps to some 
extent the other vascular glands, are, like the lymphatic 
glands, engaged in the formation of the germs of subse- 
quent blood-corpuscles. For it seems quite certain, that 
the blood of the splenic vein contains an unusually large 
amount of white corpuscles; and in the disease termed 
leucocythtemia, in ^vhich the pale corpuscles of the blood 
are remarkably increased in number, there is almost 
always found an hypertrophied state of the spleen or thy- 
roid body, or some of the lymphatic glands. Accordingly 
there seems to be a close analogy in function between the 
so-called vascular and the lymphatic glands : the former 
elaborating albuminous principles, and forming the germs 
of new blood-corpuscles out of alimentary materials ab- 
sorbed by the blood-vessels ; the latter discharging the 
like office on nutritive materials taken up by the general 
absorbent system. In Kolliker's opinion, the development 
■of colourless and also coloured corpuscles of the blood is 
one of the essential functions of the spleen, into the veins 
of which thv:; new-formed corpuscles pass, and are thus 
•conveyed into the general current of the circulation. 

There is reason to believe, too, that in the spleen many 
of the red corpuscles of the blood, those probably which 
have discharged their office and are worn out, undergo 
disintegration ; for in the coloured portion of the spleen- 
pulp an abundance of such corpuscles, in various stages of 
degeneration, are found, while the red corpuscles in the 
splenic venous blood are said to be relatively diminished. 
According to Kolliker's description of this process of dis- 
integration, the blood-corpuscles, becoming smaller and 
darker, collect together in roundish heaps, which may 
remain in this condition, or become each surrounded by a 
cell-wall. The cells thus produced may contain from one 
to twenty blood-corpuscles in their interior. These cor- 
puscles become smaller and smaller ; exchange their red 



41 8 THE DUCTLESS GLANDS. 

for a golden yellow, brown, or black colour; and, at length, 
are converted into pigment-granules, which by degrees- 
become paler and paler, until all colour is lost. The 
corpuscles undergo these changes whether the heaps of 
them are enveloped by a ceU-wall or not. 

Besides these, its supposed direct offices, the spleen is 
believed to fulfil some purpose in regard to the portal 
circulation, with which it is in close connection. From tha 
readiness with which it admits of being distended, and 
from the fact that it is generally small while gastric 
digestion is going on, and enlarges when that act is con- 
cluded, it is supposed to act as a kind of vascular reservoir, 
or diverticulum to the portal system, or more particularly 
to the vessels of the stomach. That it may serve such a 
purpose is also made probable by the enlargement which 
it undergoes in certain affections of the heart and liver^ 
attended with obstruction to the passage of blood through 
the latter organ, and by its diminution when the congestion 
of the portal system is relieved by discharges from th& 
bowels, or by the effusion of blood into the stomach.. 
This mechanical influence on the circulation, however^ 
can hardly be supposed to be more than a very subordinate 
part of the office of an organ of so great complexity as the 
spleen, and containing so many other structures besides 
blood-vessels. The same may also be said with regard to 
the opinion that the thyroid gland is important as a 
diverticulum for the cerebral circulation, or the thymus 
for the pulmonary in childhood. These, like the spleen,, 
must have peculiar and higher, though as yet ill-under~ 
stood, offices. 



419 



CHAPTER XIV. 

THE SKIX AXD ITS SECRETIOX. 

To complete the consideration of the processes of organic 
life, and especially of those which, by separating materials 
from the blood, maintain it in the state necessary for the 
nutrition of the body, the structure and functions of the 
skin must be now considered: for besides the purposes 
which it serves — (i), as an external integument for the 
protection of the deeper tissues, and (2), as a sensitive 
organ in the exercise of touch, it is also (3), an important 
excretory, and (4) an absorbing organ; while it plays a 
most important part in (5) the regulation of the tempera- 
ture of the body. 



Structure of the Skin, 

The skin consists, principally, of a layer of vascular 
tissue, named the corium, derma, or cutis vera, and an 
external covering of epithelium termed the cuticle or 
epidermis. Within and beneath the corium are imbedded 
several organs with special functions, namely sudoriparous 
glands, sebaceous glands, and hair-follicles ; and on its sur- 
face are sensitive pajnllce. The so-called appendages of 
the skin — the hair and nails — are modifications of the 
epidermis. 

Epidermis. — The epidermis is composed of several layers 
of epithelial cells of the squamous kind (p. 30), the deeper 
cells, however, being rounded or elongated, and in the 
latter instance having their long axis arranged vertically 
as regards the general surface of the skin, while the more 

E E 2 



420 



THE SKIN. 



Fig. 109.* 



superficial cells are flattened and scaly (fig. 1 09). The 

deeper part of the epider- 
mis, which is softer and 
more opaque than the su- 
perficial, is called the rete 
mucosum. Many of the 
epidermal cells contain 
pigment, and the varying 
quantity of this is the 
source of the different 
sliades of tint in the skin, 
both of individuals and 
races. The colouring mat- 
ter is contained chiefly in 
the deeper cells composing 
the rete mucosum, and be- 
comes less evident in them 
as they are gradually 
pushed up by those under them, and become, like their 
predecessors, flattened and scale-like (fig. 1 09). It is by 
this process of production from beneath, to make up for 
the waste at the surface, that the growth of the cuticle is 
effected. 

The thickness of the epidermis on different portions of 
the skin is directly proportioned to the friction, pressure, 
and other sources of injury to which it is exposed ; and the 
more it is subjected to such injury, within certain limits, 
the more does it grow, and the thicker and more horny 
does it become ; for it serves as well to protect the sen- 
sitive and vascular cutis from injury from without, as to 
limit the evaporation of fluid from the blood-vessels. The 




* Fig. 109. Skin of the negi-o, in a vertical section, magnified 250 
diameters, a, a, cutaneous papilla ; b, undermost and dark coloured 
layer of oblong vertical epidermis-cells ; c, mucous or Malpighian 
layer ; d, liorny layer (from Sharpey). 



THE COEIUM OR CUTIS VERA. 42 1 

adaptation of the epidermis to the latter purposes may be 
well shown by exposing to the air two dead hands or feet, 
of which one has its epidermis perfect, and the other is 
deprived of it ; in a day, the skin of the latter will become 
brown, dry, and horn -like, while that of the former will 
almost retain its natural moisture. 

Cutis vera. — The corium or cutis, which rests upon a layer 
of adipose and cellular tissue of varying thickness, is a 
dense and tough, but yielding and highly elastic structure, 
composed of fasciculi of fibro-cellular tissue, interwoven 
in all directions, and forming, by their interlacements, 
numerous spaces or areolae.. These areolce are large in 
the deeper layers of the cutis, and are there usually filled 
with little masses of fat (fig. 112): but, in the more super- 
ficial parts, they are exceedingly small or entirely oblite- 
rated. 

By means of its toughness, flexibility, and elasticity, the 
skin is eminently qualified to serve as the general integu- 
ment of the body, for defending the internal parts from 
external violence, and readily yielding and adapting itself 
to their various movements and changes of position. But, 
from the abundant supi)ly of sensitive nerve-fibres which 
it receives, it is enabled to fulfil a not less important pur- 
pose in serving as the principal organ of the sense of 
touch. The entire surface of the skin is extremely sen- 
sitive, but its tactile properties are due chiefly to the 
abundant papillae with "s^^hich it is studded. These papillae 
are conical elevations of the corium, with a single or 
divided free extremity, more prominent and more densely 
set at some parts than at others (figs. I lO and III). The 
parts on which they are most abundant and most prominent 
are the palmar surface of the hands and fingers, and the 
soles of the feet — parts, therefore, in which the sense of 
touch is most acute. On these parts they are disposed 
in double rows, in parallel curved lines, separated from 
each other by depressions (fig. 112). Thus they may 



422 



THE SKIX. 



be seen easily on the palm, whereon each raised line is 
composed of a double row of papilla), and is intersected by- 
short transverse lines or furrows corresponding with the 
interspaces between the successive pairs of papilla). Over 
other parts of the skin they are more or less thinly 
scattered, and are scarcely elevated above the surface. 



Flq. no.* 



Fig. iii.t 




iFfin 



Their average length is about -rro^^ ^^ ^^ inch, and at 
their base they measure about -^-jTr^^ ^^ ^^ i^<^^ ^^ diameter. 
Each papilla is abundantly supplied with blood, receiving 
from the vascular plexus in the cutis one or more minute 
arterial twigs, which divide into capillary loops in its 
substance, and then reunite into a minute vein, which 
passes out at its base. The abundant supply of blood 
which the papilla) thus receive explains the turgescence or 
kind of erection which they undergo when the circulation 
through the skin is active. The majority, but not all, of 
the papilla) contain also one or more terminal nerve -fibres, 
from the ultimate ramifications of the cutaneous plexus, 
on which their exquisite sensibility depends. The exact 
mode in which these nerve-fibres terminate is not yet 



* Fig. I ID. Papilla?, as seen with a microscope, on a portion of tlie 
true skin, from which the cuticle has been removed {after Breschet). 

+ Fig. III. Compound papillre from the palm of the hand, mag- 
nified 60 diameters ; a, basis of a papilla ; h, h, divisions or branches 
of the same ; c, c, branches belonging to papillae, of which the bases 
are hidden from view (after Kolliker). 



TOUCII-CORPUSCLES. 



423 



satisfactorily determined. In some parts, especially those 
in which the sense of touch is highly developed, as for 
•example, the palm of the hand and the lip^, the fibres 

Fig. 112.* 



e- 




appear to terminate, in many of the papilla), by one or 
more free ends in the substance of a dilated oval-shaped 
body, not unlike a Pacinian corpuscle (figs. 136, 137), 
occupying the principal part of the interior of the papillae, 
and termed a touch-corpuscle (fig. 1 13). The nature of this 
body is obscure. Kolliker, Huxley, and others, regard it as 



* Fig. 112. Vertical section of the skin and subcutaneous tissue, 
from end of tlie thumb, across the ridges and furrows, magnified 20 
diameters (from Kolliker) : a, horny, and h, mucous layer of the epi- 
dermis ; c, corium ; d, imnniculus adijwsus ; e, papillre on the ridges ; 
/, fat clusters ; g, sweat-glands ; h, sweat-ducts ; i, their openings on 
the surface. 



424 



THE SKIX. 



little else than a mass of fibrous or connective tissue, 
surrounded by elastic fibres, and formed, according to 
Huxley, by an increased development of the neurilemma 
of the nerve-fibres entering thOj papillee. Wagner, how- 
Fig. 113.* 




ever, to whom seems to belong the merit of first fully 
describing these bodies, believes that, instead of thus 
consisting of a homogeneous mass of connective tissue, 
they are special and peculiar bodies of laminated structure, 
directly concerned in the sense of touch. They do not 
occur in all the papillie of the parts where they are found, 
and, as a rule, in the papillse in which they are present 
there are no blood-vessels. Since these peculiar bodies in 
which the nerve-fibres end are only met with in the papillse 
of highly sensitive parts, it may be inferred that they are 

* Fig. 113. Papillge from the skin of the hand, freed from the cuticle 
and exhibiting the tactile corpuscles. Magnified 350 diameters, a. 
Simple papilla with four nerve-fibres : a, tactile corpuscle ; h, nerves. 
B. Papilla treated Avith acetic acid : a, cortical layer with cells and 
fine elastic filaments ; &, tactile corpuscle with transverse nuclei ; c, 
entering nei-ve with neurilemma or perineurium ; d, nerve-fibres wind- 
ing round the corpuscle, c. Papilla viewed from above so as to appear 
as a cross section : a, cortical layer ; h, nerve-fibre ; c, sheath of the- 
tactile corpuscle containing nuclei ; d, core (after KoUiker). 



TOUCH-COEPUSCLES ; EXD-BULBS. 425 

specially concerned in tlie sense of touch, yet their absence 
from the papillae of other tactile parts shows that they are 
not essential to this sense. 

Closely allied in structure to the Pacinian corpuscles 
and touch'Corpuscles are some little bodies about -^~ of 
an inch in diameter, first particularly described by Krause, 
and named by him '' end-bulbs." They are generally oval I 
or spheroidal, and composed externally of a coat of con- 
nective tissue enclosing a softer matter, in which the ex- 
tremity of a nerve terminates. These bodies have been' 
found chiefly in the lips, tongue, j)alate, and the skin of the , 
glans penis (fig. 1 14). 

Although destined especially for the sense of touch, the 
papillae are not so placed as to come into direct contact 
with external objects ; but, like the rest of the surface of 
the skin, are covered by one or more layers of epithelium, 
forming the cuticle or epidermis. The papilla) adhere 
Fig. 114.* B 







* Fig. 114. End-bulbs in papillre (magnified) treated with acetic 
acid. A, from the lips ; the white loops in one of them are capillaries. 
B, from the tongue. Two end-bulbs seen in the midst of the simple 
papillae : a, a, nerves (from Kolliker). 



426 THE SKIX. 

very intimately to the cuticle, which is thickest in the 
spaces between them, but tolerably level on its outer 
surface : hence, when stripped off from the cutis, as after 
maceration, its internal surface presents a series of pits 
and elevations corresponding to the papilla) and their 
interspaces, of which it thus forms a kind of mould. 
Besides affording by its impermeability a check to undue 
evaporation from the skin, and providing the sensitive 
cutis with a protecting investment, the cuticle is of service 
in relation to the sense of touch. For, by being thickest 
in the spaces between the papillae, and only thinly spread 
over the summits of these processes, it may serve to sub- 
divide the sentient surface of the skin into a number of 
isolated points, each of which is capable of receiving a 
distinct impression from an external body. By covering 
the papilla} it renders the sensation produced by external 
bodies more obtuse, and in this manner also is subservient 
to touch : for unless the very sensitive papilla) were thus 
defended, the contact of substances would give rise to 
pain, instead of the ordinary impressions of touch. This 
is shown in the extreme sensitiveness and loss of tactile 
power in a part of the skin when deprived of its epidermis. 
If the cuticle is very thick, however, as on the heel, touch 
becomes imperfect, or is lost, through the inability of the 
tactile i)apilla) to receive impressions through the dense 
and horny layer covering them. 

Sudoriparous Glands. — In the middle of each of the 
transverse furrows between the papilla), and irregularly 
scattered between the bases of the papilla) in those parts 
of the surface of the body in which there are no furrows 
between them, are the orifices of ducts of the sudoriparous 
or sweat glands, by which it is probable that a large portion 
of the aqueous and gaseous materials excreted by the skin 
are separated. Each of these glands consists of a small 
lobular mass, which appears formed of a coil of tubular 
gland-duct, surrounded by blood-vessels and embedded in 



SUDORIPAEOUS OE S^YEAT GLAXDS. 427 

the subcutaneous adipose tissue (fig. "" 112). From this 
nias3, the duct ascends, for a short distance, in a spiral 
manner through the deeper part of the cutis, then passing 
straight, and then sometimes again becoming spiral, it 
passes through the cuticle and opens by an oblique valve- 
like aperture. In the parts where the epidermis is thin, 
the ducts themselves are thinner and more nearly- 
straight in their course (fig. 1 1 5). The duct, which 
maintains nearty the same diameter throughout, is lined 
with a laj^er of epithelium continuous with the epidermis ; 
while the part which passes through the epidermis is com- 
posed of the latter structure only ; the cells which imme- 
diately form the boundary of the canal in this part being 
somewhat difierently arranged from those of the adjacent 
cuticle. 

The sudoriparous glands are abundantly distributed 
over the whole surface of the body; but are especially 
numerous, as well as very large, in the skin of the palm 
of the hand, where, according to Krause, they amount to 
2736 in each superficial square inch, and according to 
Mr. Erasmus Wilson, to as many as 3528. They are 
almost equally abundant and large in the skin of the sole. 
The glands by which the peculiar odorous matter of the 
axillae is secreted form a nearly complete layer under the 
cutis, and are like the ordinary sudoriparous glands, except 
in being larger and having very short ducts. In the neck 
and back, where they are least numerous, the glands 
amount to 4 1 7 on the square inch (Krause) . Their total 
number Krause estimates at 2,381,248; and, supposing 
the orifice of each gland to present a surface of ^-^-th of a 
line in diameter (and regarding a line as equal to -j-V^^ ^^ 
an inch), he reckons that the whole of the glands would 
present an evaporating surface of about eight square 
inches.'''* 

* The pecuHar bitter yellow substance secreted by the skin of the 
external auditory passage is named cerumen , and the glands themselves 



428 



THE SKIN. 



Sebaceous Glands. — Besides the perspiration, tlie skin 
Fig. 115.* secretes a peculiar fatty matter, and 

for this purpose is provided with 
another set of special organs, termed 
sebaceous glands (fig. 1 1 5), which, like 
the suboriparous glands, are abun- 
dantly distributed over most parts of 
the body. They are most numerous 
in parts largely supplied with hair, 
as the scalp and face, and are thickly 
distributed about the entrances of the 
various passages into the body, as the 
anus, nose, lips, and external ear. 
They are entirely absent from the 
palmar surface of the hands and the 
plantar surfaces of the feet. They 
are minutely lobulated glands, com- 
posed of an aggregate of small vesi- 
cles or sacculi filled with opaque 
white substances, like soft ointment. Minute capillary 
vessels overspread them; and their ducts, which have a 
bearded appearance, as if formed of rows of shells, open 
either on the surface of the skin, close to a hair, or, which 
is more usual, directly into the follicle of the hair. In 
the latter case, there are generally two glands to each hair 

(fig. 115). 




Structure of Hair and Nails. 
Hah: — A hair is produced by a peculiar growth and 



cenuninous glands ; but they do not much differ in structure from the 
ordinary sudoriparous glands. 

* Fig. 115. Sebaceous and sudoriparous glands of the skin (after 
Gurlt) : — 1, the thin cuticle ; 2, the cutis ; 3, adipose tissue ; 4, a 
hair, in its follicle (5) ; 6, Sebaceous gland, ox^ening into the follicle of 
the hair by an efferent duct ; 7, the sudoriparous gland. 



STRUCTURE OF HAIR. 429 

modification of the epidermis. Externally it is covered by 
a layer of fine scales closely imbricated, or overlapping 
like the tiles of a house, but with the free edges turned 
upwards (fig. 1 1 6, a). It is called the cuticle of the hair. 
Beneath this is a much thicker layer of elongated horny 
cells, closely packed together so as to resemble a fibrous 
structure. This, very commonly, in the human subject, 
occupies the whole of the inside of the hair ; but in some 

Fig 116.* 



Icitfllli 



cases there is left a small central space filled by a sub- 
stance called the medulla or pith, composed of small collec- 
tions of irregularly shaped cells, containing fat- and pig- 
ment-granules. 

The follicle, in which the root of each hair is contained, 
(fig. 1 1 7) forms a tubular depression from the surface of the 
skin, — descending into the subcutaneous fat, generally to 
a greater depth than the sudoriparous glands, and at 
its deepest part enlarging in a bulbous form, and often 
curving from its previous rectilinear course. It is lined 
throughout by cells of epithelium, continuous with those 
of the epidermis, and its walls are formed of pellucid 
membrane, which commonly, in the follicles of the largest 
hairs, has the structure of vascular fibro-cellular tissue. 
At the bottom of the follicle is a small papilla, or projec- 
tion of true skin, and it is by the production and out- 




I 



* Fig. 116. A, surface of a white hair, magnified 160 diameters. Tlie 
wave lines mark the upper or free edges of the cortical scales. B, 
separated scales, magnified 350 diameters (after Kolliker). 



430 



THE SKIN. 



growth of epidermal cells from the surface of this papilla 
that the hair is formed. The inner waU of the follicle is 



Fig. iiS.f 




* Fig. 117. Medium-sized liair iu its follicle, magnified 50 diameters 
(from KoUiker). a, stem cut short ; h, root ; c, knob ; d, hair cuticle ; 
«, internal, and /, external root-sheath ; gf, A, dermic coat of follicle ; 
i, papilla; Tc, k, ducts of sebaceous glands ; ?, corium ; m, mucous laj^er 
of epidermis ; 0, upper limit of internal root-sheath (from KoUiker). 

+ Fig. 118. Magnified view of the root of a hair (after Kohh-ausch). 
a, stem or shaft of hair cut across ; h, inner, and c, outer layer of the 
epidermal lining of the hair-follicle, called also the inner and outer root- 
sheath ; d, dermal or external coat of the hair-follicle, shown in part, 



STRUCTUEE OF XAILS. 43 1 

lined by epidermal cells continuous with, those covering the 
general surface of the skin ; as if indeed the follicle had 
been formed by a simple thrusting in of the surface of the 
integument (figs. 117, 1 18). This epidermal lining of the 
hair-follicle, or root-sheath of the hair, is composed of two 
layers, the inner one of which is so moulded on the 
imbricated scaly cuticle of the hair, that its inner surface 
becomes imbricated also, but of course in the opposite 
direction. When a hair is pulled out, the inner layer of 
the root-sheath and part of the outer layer also are com- 
monly pulled out with it. 

Nails. — A nail, like a hair, is a peculiar arrangement 
of epidermal cells, the undermost of which, like those of 
the general surface of the integument, are rounded or 
elongated, while the superficial are flattened, and of more 
horny consistence. That specially modified portion of the 
corium, or true skin, by which the nail is secreted, is called 
the matrix. 

The back edge of the nail, or the root as it is termed, is 
received into a shallow crescentic groove in the matrix y 
while the fron^ part is free, and projects beyond the ex- 
tremity of the digit. The intermediate portion of the nail 
rests by its broad under surface on the front part of the 
matrix, which is here called the hed of the nail. This part 
of the matrix is not uniformly smooth on the surface, but 
is raised in the form of longitudinal and nearly parallel 
ridges or laminae, on which are moulded the epidermal 
cells of which the nail is made up (fig. 119). 

The growth of the nail, like that of a hair, or of the 
epidermis generally, is effected by a constant production of 
cells from beneath and behind, to take the place of those 
which are worn or cut away. Inasmuch, however, as the 

e, imbricated scales about to form a cortical layer on the surface of the 
hair. The adjacent cuticle of the root-sheath is not represented, and 
the x^apilla is hidden in the lower part of the knob where that is repre- 
sented lighter. 



432 



THE SKIK 



Fig. 



G 



posterior edge of tlie nail, from its being lodged in a groove 

of the skin, cannot 
grow backwards, 
on additions be- 
ing made to it, 
so easily as it 
can pass in tbe 
opposite direc- 
tion, any growth 
at its hinder 
part pushes the 
whole forwards. 
At the same time 
fresh cells are 
added to its un- 
der surface, and 
thus each portion 
o^ of the •nail be- 

comes gradually thicker as it moves to the front, until, 
projecting beyond the surface of the matrix, it can receive 
no fresh addition from beneath, and is simply moved for- 
wards by the growth at its root, to be at last worn away or 
cut off. 

Excretion hy the Skin. 

The skin, as already stated, is the seat of a two-fold 
excretion ; of that formed by the sebaceous glands and hair- 
follicles, and of the more watery fluid, the siveat or perspira- 
tion, eliminated by the sudoriparous glands. 

The secretion of the sebaceous glands and hair-follicles 




* Fig. 119. Vertical transverse section tlirougli a small portion of the 
nail and mati'ix largely magnified (after Kolliker). 

A, corium of the nail-bed, raised into ridges or laminte a, fitting in 
hehveen corresponding laminse b, of the nail. B, Malpighian, and C, 
horny layer of nail : d, deepest and vertical cells ; c, upper flattened 
cells of Malpighian layer. 



THE SWEAT. 433 

^for their products cannot be separated) consists of cast-off 
epithelium-cells, with nuclei and granules, together with 
an oily matter, extractive matter, and stearin ; in certain 
parts, also, it is mixed with a peculiar odorous principle, 
which is said by Dr. Fischer to contain caproic, butyric, 
and rutic acids. It is, perhaps, nearly similar in composi- 
tion to the unctuous coating, or vernix caseosa, which is 
formed on the body of the foetus while in the uterus, and 
which contains large quantities both of olein and margarin 
(J. Davy). Its purpose seems to be that of keeping the 
skin moist and supple, and, by its oily nature, of both 
hindering the evaporation from the surface, and guarding 
the skin from the effects of the long-continued action of 
moisture. But while it thus serves local purposes, its 
removal from the body entitles it to be reckoned among 
the excretions of the skin; though the share it has in the 
purifying of the blood cannot be discerned. 

The fluid secreted by the sudoriparous glands is usually 
formed so gradually, that the watery portion of it escapes 
by evaporation as fast as it reaches the surface. But, 
during strong exercise, exposure to great external warmth, 
in some diseases, and when evaporation is prevented by the 
application of oiled silk or plaster, the secretion becomes 
more sensible and collects on the skin in the form of drops 
of fluid. A good analysis of the secretion of these glands, 
unmixed with other fluids secreted from the skin, can 
scarcely be made ; for the quantity that can be collected 
pure is very small. Krause in a few drops from the palm 
of the hand, found an acid reaction, oily matter, and mar- 
garin, with water. 

The i^erspiration of the skin, as the term is sometimes 
employed in physiology, includes all that portion of the 
secretions and exudations from the skin which passes off by 
evaporation ; the sweat includes that which may be collected 
only in drops of fluid on the surface of the skin. The two 
terms are, however, most often used synonymously ; and 



434 THE SKIX. 

for distinction, the former is called insensible perspiration : 
the latter, sejisible perspiration. The fluids are the same, 
except that the sweat is commonly mingled with various 
substances lying on the surface of the skin. The contents 
of the sweat are, in part, matters capable of assuming the 
form of vapour, such as carbonic acid and water, and in 
part, other matters which are deposited on the skin, and 
mixed with the sebaceous secretion. Thenard collected the 
perspiration in a flannel shirt which had been washed in 
distilled water, and found in it chloride of sodium, acetic 
acid, some phosphate of soda, traces of phosphate of lime, and 
oxide of iron, together with an animal substance. In sweat 
which had run from the forehead in drops, Berzelius found 
lactic acid, chloride of sodium, and chloride of ammonium. 
Anselmino placed his arm in a glass cylinder, and closed 
the opening around it with oiled silk, taking care that the 
arm touched the glass at no point. The cutaneous exhala- 
tion collected on the interior of the glass, and ran down as 
a fluid: on analysing this, he found water, acetate of 
ammonia, and carbonic acid ; and in the ashes of the dried 
residue of sweat he found carbonate, sulphate, and phos- 
phate of soda, and some potash, with chloride of sodium, 
phosphate and carbonate of lime, and traces of oxide of iron. 
Urea has also been shown to be an ordinary constituent of 
the fluid of perspiration. 

, The ordinary constituents of perspiration, may, therefore, 
\ according to Gorup-Besanez, be thus summed up : water, 
Ifat, acetic, butyric and formic acid, urea, and salts. The 
principal salts are the chlorides of sodium and potassium, 
together with, in small quantity, alkaline, and earthy phos- 
phates and sulphates ; and, lastly, some oxide of iron. Of 
these several substances, none, however, need particular 
consideration, except the carbonic acid and water. 

The quantity of watery vapour excreted from the skin 
was estimated very carefully by Lavoisier and Sequin. 
The latter chemist enclosed his body in an air-tight bag, 



EXHALATION FROM THE SKIX. 45.5 

with, a mouth-piece. The bag being closed by a strong 
band above, and the mouth-piece adjusted and gummed to 
the skin around the mouth, he was weighed, and then re- 
mained quiet for several hours, after which time he was 
again weighed. The difference in the two weights indi- 
cated the amount of loss by pulmonary exhalation. Having 
taken off the air-tight dress, he was immediately weighed 
again, and a fourth time after a cei-tain interval. The 
difference between the two weights last ascertained gave 
the amount of the cutaneous and pulmonary exhalation 
together ; by subtracting from this the loss by pulmonary 
exhalation alone, while he was in the air-tight dress, he 
ascertained the amount of cutaneous transpiration. The 
repetition of these experiments during a long period, 
showed that, during a state of rest, the average loss by 
cutaneous and pulmonary exhalation in a minute, is from 
seventeen to eighteen grains, — the minimum eleven grains, 
the maximum thirty-two grains ; and that of the eighteen 
grains, eleven pass off by the skin, and seven by the lungs. 
The maximum loss by exhalation, cutaneous and pulmo- 
nary, in twenty-four hours, is about 3 J lb. ; the minimum 
about I J lb. Valentin found the whole quantity lost by 
exhalation from the cutaneous and respiratory surfaces of 
a healthy man who consumed daily 40,000 grains of food 
and drink, to be 19,000 grains, or 2-flb. Subtracting 
from this, for the pulmonary exhalation, 5? 000 grains, 
and, for the excess 6f the weight of the exhaled carboni'' 
acid over that of the equal volume of the inspired oxygen, 
2,256 grains, the remainder, 11,744 grains, or nearly 
i^lb., may represent an average amount of cutaneous 
exhalation in the day. 

The large quantity of watery vapour thus exhaled from 
the skin, will prove that the amount excreted by simple 
transudation through the cuticle must be very large, if we 
may take Krause's estimate of about eight square inches 
for the total evaporating surface of the sudoriparous 

F F 2 



43^ THE SKIX. 

glands'; for not more than about 3,365 grains could be 
evaporated from such a surface in twenty-four hours, 
under the ordinary circumstances in which the surface of 
the skin is placed. This estimate is not an improbable 
one, for it agrees very closely with that of Milne-Edwards, 
who calculated that when the temperature of the atmo- 
sphere is not above 6S° F., the glandular secretion of the 
skin contributes only -^4h to the total sum of cutaneous 
exhalation. 

i The quantity of watery vapour lost by transpiration, is 
of course influenced by all external circumstances which 
affect the exhalation from other evaporating surfaces, such 
as the temperature, the hygrometric state, and the stillness 
of the atmosphere. But, of the variations to which it is 
subject under the influence of these conditions, no calcula- 
tion has been exactly made. 

Neither, until recently, has there been any estimate of 
the quantity of carhonic acid exhaled by the skin on an 
average, or in various circumstances. Regnault and Reiset 
attempted to supply this defect, and concluded, from some 
careful experiments, that the quantity of carbonic acid 
exhaled from the skin of a warm-blooded animal is about 
-^^^th of that furnished by the pulmonary respiration. Dr. 
Edward Smith's calculation is somewhat less than this. 
The cutaneous exhalation is most abundant in the lower 
classes of animals, more particularly the naked Am- 
phibia, as frogs and toads, whose skin is thin and moist, 
and readily permits an interchange of gases between the 
blood circulating in it and the surrounding atmosphere. 
Bischoff found that, after the lungs of frogs had been tied 
and cut out, about a quarter of a cubic inch of carbonic 
acid gas was exhaled by the skin in eight hours. And 
this quantity is very large, when it is remembered that a 
full-sized frog will generate only about half a cubic inch of 
carbonic acid by his lungs and skin together in six hours 
(Milne-Edwards and Miiller). That the respiratory func- 



ABSORPTION BY TEE SKIX. 437 

tion of the skin is, perhaps, even more considerable in the 
higher animals than appears to be the case from the ex- 
I)eriments of Regnault and Reiset just alluded to, seemed 
probable by the fact observed by Magendie and others, 
that if the skin of animals is covered with an impermeable 
varnish, or the body enclosed, all but the head, in a 
caoutchouc dress, animals soon die, as if asphyxiated; 
their heart and lungs being gorged with blood, and their 
temperatures, during life, gradually falling many degrees, 
and sometimes as much as ^6° F. below the ordinary 
standard (Magendie) . Some recent experiments of Lashke- 
witzch appear, however, to confirm the opinion of Valentin, 
that loss of temperature is the immediate cause of death in 
these cases. A varnished animal is said to have suffered 
no harm when surrounded by cotton wadding, but it died 
when the wadding was removed. 

Absorption by the skin has been already mentioned, as an 
instance in which that process is most actively accom- 
plished. Metallic preparations rubbed into the skin have 
the same action as when given internally, only in a less 
degree. ]Mercury applied in this manner exerts its specific 
influence upon syphilis, and excites salivation ; potassio- 
tartrate of antimony may excite vomiting, or an eruption 
extending over the whole body ; and arsenic may produce 
poisonous effects. Vegetable matters, also, if soluble, or 
already in solution, give rise to their peculiar effects, as 
cathartics, narcotics, and the like, when rubbed into the 
skin. The effect of rubbing is probably to convey the 
particles of the matter into the orifices of the glands 
whence they are more readily absorbed than they would 
be through the epidermis. When simply left in contact 
with the skin, substances, unless in a fluid state, are seldom 
absorbed. 

It has long been a contested question whether the skin 
covered with the epidermis has the power of absorbing 
water ; and it is a point the more difficult to determine 



438 THE SKIN. 

because the skin loses water by evaporation. But, from 
the result of many experiments, it may now be regarded 
as a well-ascertained fact that such absorption really occurs. 
M. -Edwards has proved that the absorption of water by 
the surface of the body may take place in the lower 
animals very rapidly. Not ^ only frogs, which have a thin 
skin, but lizards, in which the cuticle is thicker than in 
man, after having lost weight by being kept for some 
time in a dry atmosphere, were found to recover both their 
weight and plumpness very rapidly when immersed in 
water. When merely the tail, posterior extremities, and 
posterior part of the body of the lizard were immersed, the 
water absorbed was distributed throughout the system. 
And a like absorption through the skin, though to a less 
xtent, may take place also in man. 

Dr. Madden, having ascertained the lo^s of weight, by 
cutaneous and pulmonary transpiration, that occurred 
during half an hour in the air, entered the bath, and 
remained immersed during the same period of time, breath- 
ing through a tube which communicated with the air 
exterior to the room. He was then carefully dried and 
again weighed. Twelve experiments were performed in 
this manner; and in ten there was a gain of weight, 
varjdng from 2 scruples to 5 drachms and 4 scruples, or a 
mean gain of l drachm 2 scruples and 13 grains. The 
loss in the air during the same length of time (half an 
hour) varied in ten experiments from 2 J drachms to 
I ounce 2 J scruples, or in the mean was about 6i drachms. 
So that, admitting the supposition that the cutaneous 
transpiration was entirely suspended, and estimating the 
loss by pulmonary exhalation at 3 drachms, there was, in 
these ten experiments of Dr. Madden, an average absorp- 
tion of 4 drachms, i scruple, and 3 grains, by the surface 
of the body, during half an hour. In four experiments 
performed by M. Berthold, the gain in weight was greater 
than in those of Dr. Madden. * 



ABSORPTION BY THE SKIX. 439 

In severe cases of dysphagia, wlien not even fluids can 
be taken into the stomach, immersion in a bath of warm 
water or of milk and water may assuage the thirst ; and it 
has been found in such cases that the weight of the body 
is increased by the immersion. Sailors also, when destitute 
of fresh water, find their urgent thirst allayed by soaking 
their clothes in salt water and wearing them in that state 
but these effects may be in part due to the hindrance to 
the evaporation of water from the skin. 

The absorption, also, of different kinds of gas by the 
skin is proved by the experiments of Abernethy, Cruik- 
shank, Beddoes, and others. In these cases, of course, 
the absorbed gases combine with the fluids, and lose the 
gaseous form. Several physiologists have observed an 
absorption of nitrogen by the skin. Beddoes says, that he 
saw the arm of a negro become pale for a short time when 
immersed in chlorine ; and Abernethy observed that when 
he held his hands in oxygen, nitrogen, carbonic acid, and 
other gases contained in jars, over mercury, the volume of 
the gases became considerably diminished. 

The share which the evaporation from the skin has in 
the maintenance of the uniform temperature of the body, 
and the necessary adaptation thereto of the production of 
heat, have been already mentioned (p. 239). 



440 



CHAPTER XV. 



THE KIDNEYS AND THEIR SECRETION. 

Structure of the Kidneys. 

The kidney is covered on the outside by a rather tough, 
fibrous capsule^ which is slightly attached by its inner sur- 
face to the proper substance of the organ by means of very 
fine fibres of areolar tissue and minute blood-vessels. 
From the healthy kidney, therefore, it may be easily torn 
off without injury to the subjacent cortical portion of the 

organ. At the hilus 



Fig. 1 20. 



or 
notch of the kidney, it 
becomes continuous with 
the external coat of the 
upper and dilated part of 
the ureter. 

On making a section 
length-wise through the 
kidney (fig. 120) the main 
part of its substance is 
seen to be composed of 
two chief portions, called 
respectively the cortical 
and the medullary portion, 
the latter being also some- 
times called the 'pyramidal 
portion, from the fact of its being composed of about a 




* Fig. 120. Plan of a longitudinal section througli the pelvis and 
substance of the right kidney, 4 ; a, the cortical substance ; h, b, broad 
part of the pyramids of Malpighi ; c, c, the divisions of the pelvis 
named calyces, laid open ; c', one of these unopened ; d, summit of the 
pyramids or papillae projecting into calyces ; e, e, section of the narrow 
part of two pyramids near the calyces ; J9, pelvis or enlarged divisions of 
the lu-eter within the kidney ; u, the ureter ; s, the sinus ; 7t, the hilus. 



STRUCTUEE OF THE KIDNEY. 



441 



Fig. 12 



dozen conical bundles of urine-tubes, eacb bundle being 
called a pyramid. Tbe upper part of the duct of the 
organ, or the ureter, is dilated into what is called the pelvis 
of the kidney ; and this, again, after separating into two 
or three principal divisions, is finally subdivided into still 
smaller portions, varying in number from about 8 to 12, 
or even more, and called calyces. Each of these little 
calyces or cups, again, receives the pointed extremity or 
papilla of a pyramid. Sometimes, however, more than one 
papilla is received by a calyx. 

The kidney is a gland of the class called tubular, and 
both its cortical and medullary portions are composed 
essentially of secreting tubes, the tuhuli urini/eri, which 
by one extremity, in the cortical 
portion, end commonly in little 
saccules containing blood-ves- 
sels, called Malpighian bodies, 
and by the other open through 
the pjapillce into the pelvis of the 
kidney, and thus discharge the 
urine which Aonvs through them. 

In the pyramids they are 
chiefly straight — dividing and 
diverging as they ascend through 
these into the cortical portion ; 
while in the latter region they 
spread out more irregularly, and 
become much branched and convoluted. 

The tubuli uriniferi (fig. 121) are composed of a nearly 
homogeneous membrane, lined internally by spheroidal 
epithelium, and for the greater part of their extent are 
about -g-Z.-o of an inch in diameter, — becoming somewhat 




* Fig. 121. A. Portion of a secreting canal from the cortical sub- 
stance of the kidney, b. The epithelium or gland-cells, more highl)' 
magnified (700 times). 



44^ 



THE KIDNEYS AND THEIR SECRETION. 



larger than this immediately before they open through the 
Fig. 122.* papillcB. On tracing these tu- 

bules upwards from the papillae, 
they are found to divide dicho- 
tomously as they ascend through 
the pyramids, and on reaching 
the bases of the latter, they 
begin to branch and diverge 
more widely, and to form by 
their branches and convolutions 
the essential part of the cortical 
portion of the organ. At their 
extremities they become dilated 
into the Malpighian capsules. 
Until recently, it was believed 
that the straight tubules in the 
pyramids branch out and be- 
come convoluted immediately on 
reaching the bases of the pyra- 
mids ; but between the straight 
tubes in the pyramids and the 
convoluted tubes in the cortical 
portion, there has been shown to 
be a system of tubules of smaller diameter than either, 
which form intercommunications between the two varieties 
formerly recognised. These intervening tubules, called the 
loopeA tithes of Henle, arising from the straight tubes in 




* Fig. 122. Diagram of the looped uriniferous tubes and their con- 
nection with the capsules of the glomeruU (from Sou they, after Ludwig). 
In the lower part of the figure one of the large branching tubes is shown 
opening on a papilla ; in the middle part two of the looped small tubes 
are seen descending to form their loops, and re-ascending in the medul- 
lary substance ; while in the upper or cortical part, these tubes, after 
some enlargement, are represented as becoming convoluted an ilated 
in the capsules of glomeruli. 



STRUCTURE OF THE KIDXEY. 



443 



some part of their course, or being continued from tlieir 
extremities at the bases of the pyramids, pass down loop- 
wise in the pyramids for a longer or shorter distance, and 
then, again turning up, end in the convoluted tubes whose 
extremities are dilated into the Malpighian capsules before 
referred to (fig. 122). On a transverse section of a pyramid 
(fig. 123), these looped tubes are seen to be of much 
smaller calibre than the straight ones, which are passing 
down to open through the papillae. 

The Malpighian bodies are found only in the cortical part 
of the kidney. On a section of the organ, some of them 
are just visible to the naked eye as minute red points ; 
others are too small to be thus seen. Their average 
diameter is about -^-^ of an inch. Each of them is com- 
posed of the dilated extremity of an urinary tube, or 
Malpighian capsule, enclosing a tuft of blood-vessels. 

In connection 
with these little 
bodies the gene- 
ral distribution of 
blood-vessels to 
the kidney may be 
here considered. 

The renal ar- 
tery divides into 
several branches, 
which, passing in 
at the hilus of 
the kidney, and 
covered by a fine 
sheath of areolar 
tissue derived from the capsule, enter the substance of the 

* Fig. 123. Transverse section of a renal papilla (from KoUiker) ~. 
a, larger tubes or papillary ducts ; h, smaller tubes of Henle ; c, blood- 
vessels, distinguished by tlieir flatter ^epithelium ; d, nuclei of the 
stroma. 





444 THE KIDNEYS AND THEIE SECRETION. 

organ chiefly in tlie intervals between the papillae, and X 
penetrate the cortical substance, where this dips jiown 
between the bases of the i)yramids. Here they form a 
tolerably dense plexus of an arched form, and from this 
are given off smaller arteries which ultimately supply the 
Malpighian bodies. 

The small afferent artery (fig, 
124), which enters the Malpi- 
ghian body by perforating the 
capsule, breaks up in the interior 
into a dense and convoluted and 
looped capillary plexus, which is 
ultimately gathered up again 
into a single small efferent vessel, 
comparable to a minute vein, 
which leaves the Malpighian 
capsule just by the point at 
w^hich the afferent artery enters it. On leaving, it does 
not immediately join other small veins as might have been 
expected, but again breaking up into a network of capil- 
lary vessels, is distributed on the exterior of the tubule, 
from whose dilated end it had just emerged. After this 
second breaking up it is finally collected into a small vein, 
which, by union with others like it, helps to form the 
radicles of the renal vein. 

The Malpighian capsule is lined by a layer of fine squa- 
mous epithelial cells; but whether the small glomerulus 
or tuft of capillaries in the interior is covered by a similar 
layer is uncertain. Kolliker believes that such a covering. 




* Fig. 124. Diagram showing the relation of the Malpighian bod}- 
to the uriuiferous ducts and blood-vessels (after Bowman) : a, one of 
the interlobular arteries ; a', aiFerent artery passing into the glomerulus ; 
c, capsule of the Malpighian body, forming the termination of and con- 
tinuous with t, the uriniferous tube ; c', c', efferent vessels which sub- 
divide in the plexus p, surrounding the tube, and finally terminate in 
the branch of the renal vein e. 



STEUCTUEE OF THE KIDNEY. 



445 



although, exceedingly thin, is present, and has delineated 
the appearance in the accompanying diagram (fig. 125). 
Besides the small afferent arteries of the Malpighian 



Fig. 125.* 



bodies, there are, of course, 
others which are distri- 
buted in the ordinary 
manner, for nutrition's 
sake, to the different parts 
of the organ ; and in the 
pyramids, between the 
tubes, there are numerous 
straight vessels, the vasa 
recta, supposed by some 
observers to be branches 
of rasa efferentia from 
Malpighian bodies, and 
therefore comparable to the 
venous plexus around the tubules in the cortical portion, 
while others think that they arise directly from small 
branches of the renal arteries. 

Between tho tubes, vessels, etc., which make up the 
main substance of the kidney, there exists in small quantity 
a fine matrix of areolar tissue. 

The nerves of the kidney are derived from the renal 
plexus, f 




* Fig. 125. Semidiagrammatic representation of a Malpighian body 
in its relation to the uriniferous tube (from Kolhker) ^. a, capsule 
of the Malpighian body ; d, epithelium of the uriniferous tube ; e, de- 
tached epithelium ; /, afferent vessel ; g, efferent vessel ; h, convoluted 
vessels of the glomerulus. 

t For a more detailed account of the structure of the kidney and a 
summary of the various opinions on the subject, the student may be 
referred especially to Quain's Anatomy, 7th ed., and to a paper by 
Dr. Eeginald Southey in vol. i. of the St. Bartholomew's Hospital 
Eeports. 



446 THE KIDXEYS AND THEIR SECRETION. 

Secretion of Urine. 

The separation from tlie blood of the solids in a state 
of solution in the urine is probably effected, like other 
secretions, by the agency of the gland-cells, and equally 
in aU parts of the urine-tubes. The urea and uric acid, 
and perhaps some of the other constituents existing ready 
formed in the blood, may need only separation, that is 
they may pass from the blood to the urine without further 
elaboration; but this is not the case with some of the 
other principles of the urine, such as the acid phosphates 
and the sulphates, for these salts do not exist as such in 
the blood, and must be formed by the chemical agency of 
the cells. 

The ivatery part of the urine is probably in part sepa- 
rated by the same structures that secrete the solids, but 
the ingenious suggestion of Mr. Bowman that the water 
of the urine is mainly strained off, so to speak, by the 
Malpighian bodies, from the blood which circulates in their 
capillary tufts, is exceedingly probable; although if, as 
Kolliker and others maintain, there is an epithelial cover- 
ing to these tufts or glomeruli, it is very likely that the 
solids of the urine may be in part secreted here also. We 
may, therefore, conclude that all parts of the tubular 
system of the kidney take part in the secretion of the 
urine as a whole, but that there is a provision also in the 
arrangement of the vessels in the !Malpighian bodies for a 
more simple draining off of water from the blood when 
required. 

The large size of the renal arteries and veins permits so 
rapid a transit of the blood through the kidneys, that the 
whole of the blood is purified by them. The secretion of 
urine is rapid in comparison with other secretions, and as 
each portion is secreted, it propels that which is already in 
the tubes onwards into the pelvis of the kidney. Thence 
through the ureter the urine passes into the bladder, into 



PASSAGE OF URINE INTO THE BLADDER. 447 

wliich its rate and mode of entrance has been watclied in 
cases of ectopia vesicae, i.e., of such fissures in the anterior 
and lower part of the walls of the abdomen, and of the 
front wall of the bladder, as exposed to view its hinder wall 
together with the orifices of the ureters. Some good 
observations on such cases were made by Mr. Erichsen. 
The urine does not enter the bladder at any regular rate, 
nor is there a synchronism in its movement through the 
two ureters. During fasting, two or three drops enter the 
bladder every minute, each drop as it enters first raising 
up the little papilla on which, in these cases, the ureter 
opens, and then passing slowly through its orifice, which 
at once again closes like a sphincter. In the recumbent 
posture, the urine collects for a little time in the ureters, 
then flows gently, and, if the body be raised, runs from 
them in a stream till they are empty. Its flow is increased 
in deep inspiration, or straining, and in active exercise, and 
in fifteen or twenty minutes after a meal. 

The same observations, also, showed how fast some 
substances pass from the stomach through the circulation, 
and through the vessels of the kidneys. Ferrocyanide of 
potassium so passed on one occasion in a minute : vegetable 
substances, such as rhubarb, occupied from sixteen to 
thirty-five minutes; neutral alkaline salts with vegetable 
acids, which were generally decomposed in transitu, made 
the urine alkaline in from twenty-eight to forty-seven 
minutes. But the times of passage varied much ; and the 
transit was always slow when the substances were taken 
during digestion. 

The urine collecting in the urinary bladder is prevented 
from regurgitation into the ureters by the mode in which 
these pass through the walls of the bladder, namely, by 
their lying for between half and three-quarters of an inch 
between the muscular and mucous coats, and then turning 
rather abruptly forwards, and opening through the latter, 
it collects till the distension of the bladder is felt either 
by direct sensation, or, in ordinary cases, by a transferred 



448 THE URINE. 

sensation at and near the orifice of tlie urethra. Tiien, the 
efibrt of the will being directed primarily to the muscles of 
the abdomen, and through them (by reason of its tendency 
to act with them) to the urinary bladder, the latter, 
though its muscular walls are really composed of invo- 
luntary muscle, contracts, and expels the urine. (See also 
p. 223.) 

The Urine : its (general Properties. 

Healthy urine is a clear limpid fluid, of a pale yellow or 
amber colour, with a peculiar faint aromatic odour, which 
becomes pungent and ammoniacal when decomposition 
takes place. The urine, though usually clear and trans- 
parent at first, often becomes as it cools opaque and 
turbid^ from the deposition of part of its constituents pre- 
viously held in solution ; and this may be consistent with 
health, though it is only in disease that, in the temperar 
ture of 98° or I00°, at which it is voided, the urine is 
turbid even when first expelled. Although ordinarily of 
pale amber colour, yet, consistently with health, the urine 
may be nearly colourless, or of a brownish or deep orange 
tint, and, between these extremes, it may present every 
shade of colour. 

When secreted, and most commonly when first voided, 
the urine has a distinctly acid reaction in man and all car- 
nivorous animals, and it thus remains till it is neutralized 
or made alkaline by the ammonia developed in it by 
decomposition. In most herbivorous animals, on the con- 
trary, the urine is alkaline and turbid. The difference 
depends, not on any peculiarity in the mode of secretion, 
but on the differences in the food on which the two classes 
subsist : for when carnivorous animals, such as dogs, are 
restricted to a vegetable diet, their urine becomes pale, 
turbid, and alkaline, like that of an herbivorous animal, 
but resumes its former acidity on the return to an animal 
diet ; while the urine voided by herbivorous animals, e.g., 
rabbits, fed for some time exclusively upon animal sub- 



SPECIFIC GRAVITY OF UEIXE. 449 

stances, presents the acid reaction and other qualities of 
the urine of CarBivora, its ordinary alkalinity, being re- 
stored only on the substitution of a vegetable for the animal 
diet (Bernard). Human urine is not usually rendered 
alkaline by vegetable diet, but it becomes so after the free 
use of alkaline medicines, or of the alkaline salts with car- 
bonic or vegetable acids ; for these latter are changed into 
alkaline carbonates previous to elimination by the kidneys. 
Exce^^t in these cases, it is very rarely alkaline, unless 
ammonia has been developed in it by decomposition com- 
mencing before it is evacuated from the bladder. 

The average specific gravity of the human urine is about 
1020. Probably no other animal fluid presents so many 
varieties in density within twenty-four hours as the ujine 
does ; for the relative quantity of water and of solid 
constituents of which it is composed is materially influ- 
enced by the condition and occupation of the body during 
the time at which it is secreted, by the length of time 
which has elapsed since the last meal, and by several 
other accidental circumstances. The existence of these 
causes of difie-^ence in the composition of the urine has 
led to the secretion being described under the three 
heads of urina sanguinis, urina potus, and urina cibi. The' 
first of these names signifies the urine, or that part of it 
which is secreted from the blood at times in which neither 
food nor drink has been recently taken, and is applied 
especially to the urine wliich is evacuated in the morning 
before breakfast. The urina potus indicates the urine 
secreted shortly after the introduction of any considerable 
quantity of fluid into the body : and the urina cibi the por^ 
tions secreted during the period immediately succeeding a 
meal of solid food. The last kind contains a larger quantity 
of solid matter than either of the others; the first or 
second, being largely diluted with water, possesses a com- 
paratively low specific gravity. Of these three kinds, the 
morning urine is the best calculated for analysis, since it 
represents the simple secretion unmixed with the elements 

G G 



450 



THE URIXE. 



of food or drink ; if it be not used, the whole of the nrine 
passed during a period of twenty-four hours should be 
taken. In accordance with the various circumstances 
above mentioned, the specific gravity of the urine may, 
consistently with health, range widely on both sides of 
the usual average. 



The 
015 



average healthy range may 
be stated at from 10 1 5 in the winter to 1025 in the 
summer, and variations of diet and exercise may make as 
great a difference. In disease, the variation may be 
greater; sometimes descending, in albuminuria, to T004, 
and frequently ascending in diabetes, when the lU'ine is 
loaded with sugar, to 1050, or even to 1060. 

The whole quantity of urine secreted in twenty-four 
hours is subject to variation according to the amount of 
fluid drunk, and the proportion of the latter passing off 
from the skin, lungs, and alimentary canal. It is because 
the secretion of the skin is more active in summer than in 
winter, that the quantity of urine is smaller, and its 
specific gravity proportionately higher. On taking the 
mean of numerous observations by several experimenters. 
Dr. Parkes found that the average quantity voided in 
twenty-four hours by healthy male adults from twenty to 
\ forty years of age, amounted to 52 J fluid ounces. 

Chemical Composition of the Urine. 

The urine consists of water, holding in solution certain 
animal and saline matters as its ordinary constituents, and 
occasionally various matters taken into the stomach as 
food — salts, colouring matter, and the like. The quan- 
tities of the several natural and constant ingredients of 
the urine are stated somewhat differently by the different 
chemists who have analysed it ; but many of the differences 
are not important, and the well-known accuracy of the 
several chemists renders it almost immaterial which of the 
analyses is adopted. The analysis by A. Becquerel being- 
adopted by Dr. Prout, and by Dr. Golding Bird, will be 
here employed. (Table I.) 



COMPOSITION OF URINE. 



451 



Table II. has been compiled from the observations of 
Dr. Parkes, and of numerous other authors quoted in his 
admirable work on the urine. 

Table I. * 

Average quantity of each constituent of the Urine in 
1000 parts. 

Water . 967* 

Urea i4'23o 

Uric acid .' . . '468 



Colouring matter 

Mucus, and animal extractive matter 
(• Soda ^ 



inseparable from 
each other 



Salts ( 



Silica 



Sulphates 
Bi-x)hosphates 



( Potash 
( Lime 
)Soda 
) Magnesia 
( Ammonia 
( Sodium 
) Potassium 
Hippurate of soda 
Fluoride of potassium 



Chlorides 



10-167 



8-135 



traces. 



Table II. 
Averar/e quantity of the chief constituents of the Urine excreted 
in 24 hours by healthy male adults. 

Water 52 ' fluid ounces. 

Urea 512-4 gi-ains. 

Uric acid ....... 8-5 ,, 

Hippuric acid, uncertain, probably 10 to 15* ,, 



Sulphuric acid 

Phosphoric acid 

Clilorine 

Chloride of Ammonium 

Potash. 

Soda 

Lime .... 

Magnesia . 

Mucus 

Creatin 



Extractives 



Creatinin 



\ Pigment 
I Xanthin 
VHypoxanthin 
Resinous matter, 
etc. 



31-11 

45" 
105-0 

35-25 
58- 
125- 
3 '5 



:54'o 



V, G 2 



45: 



THE UEINE. 



From these proportions, however, most of the consti- 
tuents are, even in health, liable to variations. Especially 
the tvater is so. Its variations in different seasons, and 
according to the quantity of drink and exercise, have 
already been mentioned. It is also liable to be influenced 
by the condition of the nervous system, being sometimes 
greatly increased in hysteria, and some other nervous 
affections; and at other times diminished. In some 
diseases it is enormously increased ; and its increase may 
be either attended with an augmented quantity of solid 
matter, as in ordinary diabetes, or may be nearly the sole 
change, as in the affection termed diabetes insipidus. In 
other diseases, e.g., the various forms of albuminuria, the 
quantity may be considerably diminished. A febrile con- 
dition almost always diminishes the quantity of water; 
and a like diminution is caused by any affection which 
draws off a large quantity of fluid from the body through 
any other channel than that of the kidneys, e.r/.^ the bowels 
and the skin. 

Ui-ea. — Urea is the prin- 
cipal solid constituent of the 
urine, forming nearly one- 
half of the whole quantity of 
solid matter. It is also the 
most important ingredient, 
since it is the chief substance 
by which the nitrogen of de- 
composed tissue and super- 
fluous food is excreted from 
the body. For its removal, 
the secretion of urine seems 
especially provided ; and by its retention in the blood the 
most pernicious effects are produced. 

Urea, like the other solid constituents of the urine. 




* Fifj. 126. Crystals of urea. 



UREA. 



453 



exists in a state of solution. But it may be procured in 
the solid state, and then appears in the form of delicate 
silvery acicular crystals, which, under the microscope, 
appear as four-sided prisms (fig. 126). It is obtained in 
this state by evaporating urine carefully to the consistence 
of honey, acting on the inspissated mass with four parts 
of alcohol, then evaporating the alcoholic solution, and 
purifying the residue by repeated solution in water or 
alcohol, and finally allowing it to crystallise. It readily 
combines with an acid, like a weak base ; and may thus be 
conveniently procured in the form of a nitrate, by adding 
about half a drachm of pure nitric acid to double that 
quantity of urine in a watch glass. The crystals of nitrate 
of urea are formed more rapidly if the urine have been 
previously concentrated by evaporation. 

Urea is colourless when pure ; when impure, yellow or 
brown : without smell, and of a cooling, nitre-like taste ; 
has neither an acid nor an alkaline re- action, and deli- 
quesces in a moist and warm atmosphere. At 59° F. it 
requires for its solution less than its weight of water ; it is 
dissolved in all proportions by boiling water ; but it re- 
quires five times its weight of cold alcohol for its solution. 
At 24 8° F. it melts without undergoing decomposition ; at 
a still higher temperature ebullition takes place, and car- 
bonate of ammonia sublimes ; the melting mass gradually 
acquires a pulpy consistence ; and, if the heat is carefully 
regulated, leaves a grey-white powder, cyanic acid. 

Urea is identical in composition with cyanate of ammo- 
nia, and was first artificially produced by Wohler from this 
substance. Thus : — 

Cyanate of Ammonia. Urea. 

CHNO. H3N = CH^X„_0. 
- The action of heat upon urea in evolving carbonate of 
ammonia, and leaving cyanic acid, is thus explained. A 
similar decomposition of the urea with development of 
carbonate of ammonia ensues spontaneously when urine is 



454 THE URIXE. 

kept for some days after being voided, and explains the 
ammoniacal odour then evolved. It is probable, that this 
spontaneous decomposition is accelerated by the mucus and 
other animal matters in the urine, which, by becoming 
putrid, act the part of a ferment and excite a change of 
composition in the surrounding compounds. It is chiefly 
thus that the urea is sometimes decomposed before it 
leaves the bladder, when the mucous membrane is diseased, 
and the mucus secreted by it is both more abundant and, 
probably, more prone than usual to become putrid. The 
same occurs also in some affections of the nervous system, 
particularly in paraplegia. 

The quantity of urea excreted is, like that of the urine 
itself, subject to considerable variation. It is materially 
influenced by diet, being greater when animal food is 
exclusively used, less when the diet is mixed, and least of 
all with a vegetable diet. As a rule, men excrete a larger 
quantity than women, and persons in the middle periods of 
life a larger quantity than infants or old people (Lecanu\ 
The quantity of urea does not necessarily increase and 
decrease with that of the urine, though on the whole it 
would seem that whenever the amount of urine is much 
augmented, the quantity of urea also is usually increased 
(Becquerel) ; and it appears from observations of Genth, 
that the quantity of urea, as of urine, may be especially 
increased by drinking large quantities of water. In various 
diseases, as albuminuria, the quantity is reduced consider- 
ably below the healthy standard, while in other affections 
it is above it. 

The urea appears to be derived from two different sources. 
That it is derived in part from the unassimilated elements 
of nitrogenous food, circulating with the blood, is shown 
in the increase which ensues on substituting an animal or 
highly nitrogenous for a vegetable diet j in the much larger 
amount, nearly double, excreted by Carnivora than Her- 
bivora, independent of exercise ; and in its diminution to 



UEEA. 



455 



about one-half during starvation, or during the exclusion 
of non-nitrogenous principles of food. But that it is in , 
larger part derived from the disintegration of the azotized 
animal tissues, is shown by the fact that it continues to be 
excreted, though in smaller quantity than usual, when all! 
nitrogenous substances are strictly excluded from the food, 
as when the diet consists for several days of sugar, starch, 
gum, oil, and similar non-azotized vegetable substances! 
(Lehmann). It is excreted also, even though no food at ! 
all be taken for a considerable time ; thus it is found in 
the urine of reptiles which have fasted for months ; and 
in the urine of a madman, who had fasted eighteen days, 
Lassaigne found both urea and all the components of 
healthy urine. Probably aU the nitrogenous tissues fur- 
nish a share of urea by their decomposition. 

It has been commonly taken for granted that the quan- 
tity of urea in the urine is greatly increased by active 
exercise; but numerous observers have failed to detect 
more than a slight increase under such circumstances ; 
and our notions concerning the relation of this excretory 
product to the destruction of muscular fibre, consequent 
on the oxercise of the latter, have lately undergone con- 
siderable modification. There is no doubt, of course, that 
like all parts of the body, the muscles have but a limited 
term of existence, and are being constantly renewed, at 
the same time that a part of the products of their disin- 
tegration appears in the urine in the form of urea. But the 
waste is not so fast as it has been frequently supposed to 
be; and the theory that the amount of work done by 
the muscle is expressed by the quantity of urea excreted 
in the urine, and that each act of contraction corresponds 
to an equivalent waste of muscle-structure, is founded on 
error. (See also chapter on Motion.) 

Urea exists ready-formed in the blood, and is simply 
abstracted therefrom by the kidneys. It may be detected 
in small quantity in the blood, and in some other parts of 



456 THE URINE. 

the body, e.g.^ the humours of the eye (Millon), even while 
the functions of the kindeys are unimpaired : but when 
from any cause, especially extensive disease or extirpation 
of the kidneys, the separation of urine is imperfect, the 
urea is found largely in the blood and in most other fluids 
of the bod3\ 

Uric Acid, — This, which is another hitrogenous animal 

substance, with the for- 
mula C^N^H^O,, and was 
formerly termed lithic acid, 
on account of its existence 
in many forms of urinary 
calculi, is rarely absent 
from the urine of man or 
animals, though in the 
feline tribe it seems to 
be sometimes entirely re- 
placed by urea (G. Bird). 
Its proportionate quantity 
varies considerably in different animals. In man, and 
Mammalia generally, especially the Herbivora, it is com- 
paratively small. In the whole tribe of birds and of 
serpents, on the other hand, the quantity is very large, 
greatly exceeding that of the urea. In the urine of grani- 
vorous birds, indeed, urea is rarely if ever found, its place 
being entirely supplied by uric acid. The quantity of uric 
■ acid, like that of urea, in human urine, is increased by the 
use of animal food, and decreased by the use of food free 
from nitrogen, or by an exclusively vegetable diet. In 
most febrile diseases, and in i)lethora, it is formed in 
unnaturally large quantities ; and in gout it is deposited 
I in, and in the tissues around, joints, in the form of urate 
\ of soda, of which the so-called chalk-stones of this disease 
' are principally composed. 

* Fig. 127. Various forms of uric acid crystals. 




UEIC ACID. 457 

The condition in which, uric acid exists in solution in the 
urine has formed the subject of some discussion, because 
of its difficult solubility in water. 

According to Liebig the uric acid exists as urate of soda, 
produced, he supposes, by the uric acid, as soon as it is 
formed, combining with part of the base of the alkaline 
phosphate of soda of the blood. Hippuric acid, which 
exists in human urine also, he believes, acta upon the 
alkaline phosphate in the same way, and increases still 
more the quantity of acid phosphate, on the presence of 
which it is probable that a part of the natural acidity of 
the urine depends. It is scarcely possible to say whether 
the union of uric acid with the base soda and probably 
ammonia, takes place in the blood, or in the act of secre- 
tion in the kidney : the latter is the more probable 
opinion ; but the quantity of either uric acid or urates in 
the blood is probably too small to allow of this question 
being solved. 

The source of uric acid is probably in the disintegrated 
elements of albuminous tissues. The relation which uric 
acid and urea bear-to each other is, however, still obscure. 
The fact that they often exist together in the same urine, 
makes it seem probable that they have different origins or 
different offices to perform ; but the entire replacement of 
either by the other, as of urea by uric acid in the urine of 
birds, serpents, and many insects, and of uric acid by urea, 
in the urine of the feline tribe of Mammalia, shows that 
each alone may discharge all the important functions of 
the two. 

Owing to its existence in combination in healthy urine, 
uric acid for examination must generally be precipitated 
from its bases by a stronger acid. Frequently, however, 
when excreted in excess, it is deposited in a crj-stalline 
form (fig. 127), mixed with large quantities of urate of 
ammonia or soda (fig. 1 30). In such cases it maybe 
procured for microscopic examination, by gently warming 



458 



THE URINE. 



the portion of urine containing the sediment ; this dissolves 
urate of ammonia and soda, while the comparatively in- 
soluble crystals of uric acid subside to the bottom. 

The most common form in which uric acid is deposited 
in urine, is that of a brownish or yellowish powdery sub- 
stance, consisting of granules of urate of ammonia or soda. 
When deposited in crystals, it is most frequently in 
rhombic or diamond-shaped lamina), but other forms are 
not uncommon (fig. 1 27). When deposited from urine, 
the crystals are generally more or less deeply coloured, 
by being combined with the colouring principles of the 
urine. 



Fig. 128. 



Hippuric Acid has long 
been known to exist in the 
urine of herbivorous animals 
in combination with soda. 
Liebig has shown that it also 
exists naturally in the urine 
of man, in quantity equal to 
the uric acid, andWeismann's 
observations agree with this. 
It is a nitrogenous compound 
with the formula CjjHgNOg. 
It is closely allied to benzoic 
acid ; and this substance when introduced into the system, 
is excreted by the kidneys as hippuric acid (Ure). Its 
source is not satisfactorily determined : in part it is pro- 
bably derived from some constituents of vegetable diet, 
though man has no hippuric acid in his food, nor, com- 
monly, any benzoic acid that might be converted into it ; 
in part from the natural disintegration of tissues, inde- 
pendent of vegetable food, for Weismann constantly found 
an appreciable quantity, even when living on an exclusively 
animal diet. 




Fig. 128. Crystals of hippuric acid. 



COLOUEING MATTER : MUCUS : EXTRACTIVE. 



459 




The nature and composition of the colouring matter of 
urine are involved in some obscurity. It is probably closely 
related to the colouring matter of the blood. 

The mucus in the urine con- jrig^ 129.* 

sists principally of the epi- 
thelial debris of the mucous 
surface of the urinary pas- 
sages. Particles of epithe- 
lium, in greater or less abun- 
dance, maybe dectectedinmost 
samples of urine, especially if 
it has remained at rest for 
some time, and the lower 
strata are then examined (fig. 
129). As urine cools, the 
mucus is sometimes seen suspended in it as a delicate opaque 
cloud, but generally it falls. In inflammatory affections of 
the urinary passages, especially of the bladder, mucus in 
large quantities is poured forth, and speedily undergoes 
decomposition. The presence of the decomposing mucus 
excites (as already stated) chemical changes in the urea, 
whereby ammonia, or carbonate of ammonia, is formed, 
which, combining with the excess of acid in the super- 
phosphates in the urine, produces insoluble neutral or 
alkaline phosphates of lime and magnesia, and phosphate 
of ammonia and magnesia. These, mixing with the mucus, 
constitute the peculiar white, viscid, mortar-like substance 
which collects upon the mucous surface of the bladder, and 
is often passed with the urine, forming a thick, tenacious 
sediment. 

Besides mucus and colouring matter, urine contains a 
considerable quantity of animal matter, usually described 
under the obscure name of animal extractive. The investi- 
gations of Liebig, Heintz, and others, have shown that 



Fig. 129. Mucus deposited from urine. 



460 THE TJRIXE. 

some of this ill-defined substance consists of Creat'm and 
Creatiniii, two crystallizable substances derived, probably, 
from the metamorphosis of muscular tissue. These sub- 
stances appear to be intermediate between the proper 
elements of the muscles, and, perhaps, of other azotized 
tissues and urea : the first products of the disintegrating 
tissues probably consisting not of urea, but of Creatin and 
Creatinin, which subsequently are partly resolved into 
urea, partly discharged, without change, in the urine. 
The names of some other substances of which there are 
commonly traces in the urine, will be found in Table II., 
p. 45 I . It has been shown by Scherer that much of the 
substance classed as extractive matter of the urine, is the 
peculiar colouring matter, probably derived from the 
hfemo-globin of the blood. 

Saline Matter. — The sulphuric acid in the urine is com- 
bined chiefly or entirely with soda, and potash : forming 
salts which are taken in very small quantity with the food, 
and are scarcely found in other fluids or tissues of the 
body ; for the sulphates commonly enumerated among the 
constituents of the ashes of the tissues and fluids are, for 
the most part or entirely, produced by the changes that 
take place in the burning. Dr. Parkes, indeed, considers 
that only about one-third of the sulphuric acid found in 
the urine is derived directly from the food. Hence the 
greater part of the sulphuric acid which the sulphates in 
the urine contain, must be formed in the blood, or in the 
act of secretion of urine ; the sulphur of which the acid is 
formed, being probably derived from the decomposing 
nitrogenous tissues, the other elements of which are re- 
solved into urea and uric acid. It may be in part derived 
also, as Dr. Parkes observes, from the sulphur-holding 
taurin and cystin which can be found in the liver, lungs, 
and other parts of the body, but not generally in the 
excretions ; and which, therefore, must be broken up. The 
oxygen is supplied through the lungs, and the heat gene- 



ALKALIXE AXD EARTHY PHOSPHATES. 461 

rated during combination with the sulphur, is one of the 
subordinate means by which the animal temperature is 
maintained. 

Besides the sulphur in these salts, some also appears to 
be in the urine, uncombined with oxygen ; for after all the 
sulphates have been removed from urine, sulphuric acid 
may be formed by drying and burning it with nitre. Mr. 
Ronalds believes that from three to five grains of sulphur 
are thus daily excreted. The combination in which it 
exists is uncertain : possibly it is in some compound 
analogous to cystin or cystic oxide (p. 462). 

The j^Jiosjjhoric acid in the urine is combined partly with 
the alkalies, partly with the alkaline earths — about four or 
five times as much with the former as with the latter. In 
blood, saliva, and other alkaline fluids of the body, phos- 
phates exist in the form of alkaline, or neutral acid salts. 
In the urine they are acid salts, viz., the phosphates of 
sodium, ammonium, calcium and magnesium, the excess 
of acid being, according to Liebig, due to the appropriation 
of the alkali with which the phosphoric acid in the blood 
is combined, by the several new acids which are formed or 
discharged at the kidneys, namely, the uric, hippuric, and 
sulphuric acids, all of which he supposes to be neutralized 
with soda. 

The presence of the acid phosphates accounts, in great 
measure, or, according to Liebig, entirely, for the acidity 
of the urine. The phosphates are taken largely in both 
vegetable and animal food ; some thus taken, are excreted 
at once ; others, after being transformed and incorporated 
with the tissues. Phosphate of calcium forms the principal 
earthy constituent of bone, and from the decomposition of 
the osseous tissue the urine derives a large quantity of this 
salt. The decomposition of other tissues also, but espe- 
cially of the brain and nerve-substance, furnishes large 
supplies of phosphorus to the urine, which phosphorus is 
supposed, like the sulphur, to be united with oxygen, and 



462 



THE URIXE. 




then combined with bases. This quantity is, however, 

„. * liable to considerable vari- 

Fig. 130.* 

ation. Any undue exercise of 
the mind, and all circum- 
stances producing nervous 
exhaustion, increase it. The 
earthy phosphates are more 
abundant after meals, whe- 
ther on animal or vegetable 
food, and are diminished after 
long fasting. The alkaline 
phosphates are increased after 
animal food, diminished after 
vegetable food. Exercise increases the alkaline, but not 
the earthy phosphates (Bence Jones). Phosphorus uncom- 
bined with oxygen appears, like sulphur, to be excreted in 
the urine (Ronalds). When the urine undergoes alkaline 
fermentation, phosphates are deposited in the form of an 
urinary sediment consisting chiefly of phosphate of ammonia 
and magnesia (triple phosphate) (fig. 1 30). This compound 
does not, as such, exist in healthy urine. The ammonia is 
chiefly or wholly derived from the decomposition of urea 

(p. 453)- 

The chlorine of the urine occurs chiefly in combination 
with sodium, but slightly also with ammonium, and, 
perhaps, potassium. As the chlorides exist largely in 
food, and in most of the animal fluids, their occurrence in 
the urine is easily understood. 

Cystin (fig. 1 32) is an occasional constituent of urine. It 
resembles taurin in containing a large quantity of sulphur — 
more than 25 per cent. It does not exist in healthy urine. 

Another common morbid constituent of the urine is 



* Fig. 130. Urinary sediment of triple phosphates (large prismatic 
crystals) and urate of ammonia, from urine which had undergone 
alkaline fermentation. 



THE NERVOUS SYSTEM. 463 

oxalic acid, whick is frequently deposited in combination 
Fig. 131.* Fig. 132.! 




with, lime (fig. 131) as an urinary sediment. Like cystin, 
but much more commonly, it is the chief constituent of 
certain calculi. 

A small quantity of gas is naturally present in the urine 
in a state of solution. It consists chiefly of carbonic acid 



and nitrogen. 



CHAPTER XVI. 

THE NERYOUS SYSTEM. 



The nervous system consists of two portions or systems, 
the cerebrospinal and the sympathetic or gamjUonic, each of 
which (though they have many things in common) pos- 
sesses certain peculiarities in structure, mode of action, and 
range of influence. 

The cerebrospinal system includes the brain and spinal 
cord, with the nerves proceeding from them, and the several 
ganglia seated upon these nerves, or forming part of the 



* Fig. 131. Crystals of oxalate of lime. 
+ Fig. 132. Crystals of cystin. 



464 THE NERVOUS SYSTEM. 

substance of tlie brain. It was denominated by Bichat 
the nervous system of animal life ; and includes all tlie 
nervous organs in and through which are performed the 
several functions with which the mind is more immediately 
connected, namely, those relating to sensation and volition, 
and the mental acts connected with sensible things. 

The sympathetic or ganglionic portion of the nervous sys- 
tem, which Bichat named the nervous system of organic'^' 
life, consists essentially of a chain of ganglia connected 
by nervous cords, which extend from the cranium to the 
pelvis, along each side of the vertebral column, and from 
which, nerves with ganglia proceed to the viscera in the 
thoracic, abdominal, and pelvic cavities. By its distribu- 
tion, as well as by its peculiar mode of action, this system 
is less immediately connected with the mind, either as con- 
ducting sensations or the impulses of the will ; it is more 
closely connected than the cerebro -spinal system is with 
the processes of organic life. 

The differences, however, between these two systems, 
are not essential : their actions differ in degree and object 
more than in kind or mode. 

Elementai-y Structures of the Nervous System. 
The organs of the nervous system or systems are com- 
posed essentially of two kinds of structure, vesicular and 
fibrous ; both of which appear essential to the construction 
of even' the simplest nervous system. The vesicular 

* The term organic is often used in connection with a function, 
such as digestion or secretion, which belongs to all organised beings 
alike ; while the term animal function, or animal life, is used in con- 
nection with such qualities as volition or motion, which seem altogether 
or in gi-eat part to belong only to animals. The terms which have been 
thus used in this general way, are often loosely applied to special 
tissues. Thus organic nerve-fibres are those which are distributed 
especially to organs concerned in the discharge of the functions of 
organic, as distinguished from animal life ; and the term is still more 
commonly applied to one kind of muscular fibre. 



STRUCTFRE OF NERVE-FIBRES. 465 

structure is usually collected in masses, and mingled with, 
the fibrous structure, as in the brain, spinal cord, and the 
several ganglia ; and these masses constitute what are 
termed nerve-centres ^ being the organs in which it is sup- 
posed that nervous force may be generated, and in whicli 
are accomplished all the various reflections and otHer 
modes of disposing of impressions when they are not simply 
conducted along nerve-fibres. The fibrous nerve- substance, 
besides entering into the composition of the nervous centres, 
forms along the nerves, or cords of communication, which 
connect the various nervous centres, and are distributed in 
the several parts of the body, for the purpose of conveying 
nervous force to them, or of transmitting to the nervous 
centres the impressions made by stimuli. 

Along the nerve-fibres impressions or conditions of ex- 
citement are simply conducted : in the ^nervous centres they 
may be made to deviate from their direct course, and be 
variously diffused, reflected, or otherwise disposed of. 

Nerves are constructed of minute fibres or tubules full of 
nervous matter, arranged in parallel or interlacing bundles, 
which bundles are connected by intervening connective 
tissue, in which their principal blood-vessels ramify. A 
layer of the areolar, or of strong fibrous tissue, also sur- 
rounds the whole nerve, and forms a sheath or neurilemma 
for it. In most nerves, two kinds of fibres are mingled ; 
those of one kind being most numerous in, and charac- 
teristic of, nerves of the cerebro-spinal system; those of 
the other, most numerous in nerves of the sympathetic 
system. 

The fibres of the first kind appear to consist of tubules 
of a pellucid simple membrane, within which is contained 
the proper nerve substance, consisting of transparent oil- 
like, and apparently homogeneous, material, which gives 
to each fibre the appearance of a fine glass tube filled with 
a clear transparent fluid (fig. 133, a). This simplicity of 



466 



THE NERVOUS SYSTEM. 



composition is, however, only apparent in the fibres of 
a perfectly fresh nerve; for, shortly after death, they 
undergo changes which make it probable that their con- 
tents are composed of two different materials. The internal 
or central part, occupying the axis of the tube, becomes 
greyish, while the outer, or cortical portion, becomes 
opaque and dimly granular or grumous, as if from a kind 
of coagulation. At the same time, the fine outline of the 
previously transparent cylindrical tube is exchanged for a 
dark double contour (fig. 133, b), the outer line being 
formed by the sheath of the fibre, the inner by the margin 
of curdled or coagulated medullary substance. The gra- 
Fig- I33-* nular material shortly collects 

into little masses, which distend 
portions of the tubular mem- 
brane, while the intermediate 
spaces collapse, giving the fibres 
a varicose, or beaded appearance 
(fig. 133, c and d), instead of the 
previous cylindrical form. 

The difierence produced in the 
contents of the nerve-fibres when 
exposed to the same conditions, 
has, with other facts, led to the 
opinion now generally adopted, 
\ II /j if/ //I that the central part or axis- 
I [ K ll 1 ([ \ cylinder of each nerve-fibre difi'ers 
from the outer | portion. The 
outer portion is usually called the medullary or vcliite 



* Fig. 133. Primitive nerve-tubiiles. A. A perfectly fresh tubule 
with a single dark outline, b. A tubule or fibre with a double contour 
from commencing post-mortem change, c. The changes further ad- 
vanced, producing a varicose or beaded appearance, d. A tubule or 
fibre, the central part of which, in consequence of still further changes, 
has accumulated in separate portions witliin the sheath (after Wagner). 



STRUCTURE OF NERVE-FIBRES. 467 

substance of Schwann, being* that to which the peculiar 
white aspect of cerebro-spinal nerves is principally due. 
The whole contents of the nerve-tubules appear to be ex- 
tremely soft, for when subjected to pressure they readily 
pass from one part of the tubular sheath to another, 
and often cause a bulging at the side of the membrane. 
They also readily escape, on pressure, from the ex- 
tremities of the tubule, in the form of a grumous or 
granular material. 

That there is an essential difference in chemical com- 
position between the central and circumferential parts of 
the nerve-fibre, i.e., between the axis-cylinder and the 
medullary sheath, has of late been clearly shown by Messrs. 
Lister and Turner. Their observations, founded on Mr. 
Lockhart Clarke's method of investigating nervous sub- 
stance by means of chromic acid and carmine, have shown 
that the axis-cylinder of the ' nerve-fibre is unaffected by 
chromic acid, but imbibes carmine with great facility, 
while the medullary sheath is rendered opaque and brown 
and laminated by chromic acid, but is entirely untinged 
by the carmine. From this difference in their chemical 
behaviour, the central and circumferential portions of 
the nerve -fibres are readily distingushed on microscopic 
examination, the former being indicated by a bright red 
carmine-coloured-point, the latter by a pale ring surround- 
ing it. The laminated character of the medullary sheath 
after treatment with chromic acid is believed by Mr. 
Lockhart Clarke to be due to corrugations effected by 
the acid, and not to its having a fibrous structure, as 
maintained by Stilling. 

The size of the nerve-fibres varies, and the same fibres 
'do not preserve the same diameter through their whole 
length, being largest in their course within the trunks 
and branches of the nerves, in which the majority measure 
from -^yVo- ^0 -JuVir ^^ ^^ ^^^^ ^^ diameter. As they ap- 
proach the brain or spinal cord, and generally also in 

H II 2 



468 



THE NERVOUS SYSTEM. 



the tissues in which they are distributed, they gradually 
become smaller. In the grey or vesicular substance of the 
brain or spinal cord, they generally do not measure more 
than from -„ io o to -^-^o of an inch. 

The fibres of the second kind (fig. 134), which constitute 
the whole of the branches of the olfactory nerves, the prin- 
cipal part of the trunk and branches of the sympathetic 
nerves, and are mingled in various proportions in the 
cerebro-spinal nerves, differ from the preceding, chiefly in 
their fineness, being only about i or J as large in their 
course within the trunks and branches of the nerves ; in 

Fi(j. 134.* 




the absence of the double contour ; in their contents being 
apparently uniform ; and in their having, when in bundles, 
a yellowish-grey hue instead of the whiteness of the 
cerebro-spinal nerves. These peculiarities make it pro- 
bable that they differ from the other nerve-fibres in not 
possessing the outer layer of white or medullary nerve- 
substance ; and that their contents are composed exclusively 



* i 



* Fig. 134. Grey, pale, or gelatinous nerve-fibres (from Max 
Schult;^e), magnified between 400 and 500 diameters. A, from a 
branch of the olfactory nerve of the sheep ; a, a, two dark-bordered 
or white fibres from the fifth pair, associated with the pale olfactory 
fibres. B, from the sympathetic nerve. 



COURSE OF NER.VE-FIBEES. 



469 



of tlie substance corresponding with the central portion, or 
axis-cylinder of the larger fibres. Yet since many nerve- 
fibres may be found which appear intermediate in character 
between these two kinds, and since the large fibres, as 
they approach both their central and their peripheral end, 
gradually diminish in size, and assume many of the other 
characters of the fine fibres of the sjnnpathetic system, it 
is not necessary to suppose that there must be a material 
diiference in the office or mode of action of the two kinds 
of fibres. 

Every nerve-fibre in its course proceeds uninterruptedly 
from its origin at a nervous centre to near its destination, 

Fig. 135*. 




whether this be the periphery of the body, another nervous 
•centre, or the same centre whence it issued. 



* Fig. 135. Small branch of a muscular nerve of the frog, near its 
termination, showing divisions of the fibres. «, into two ; h, into 
three ; magnified 350 diameters (from Kolliker). 



470 



THE XEHYOUS SYSTEM. 



Bundles, or fasciculi of fibres, run together in the nerves, 
but merely lie in apposition with each other ; they do not 
unite : even when the fasciculi anastomose, there is no 
union of fibres, but only an interclicnuje of fibres between 
the anastomosing fasciculi. Although each nerve-fibre is 
thus single and undivided through nearly its whole course, 
yet as it approaches the region in which it terminates, 
individual fibres break up into several subdivisions (fig. 
135) before their final ending in the diff'erent fashions 
to be immediately described. The white or medullated 
nerve-fibres (fig. 1 33), moreover, lose their medullary sheath 
or white substance of Schwann before their final distribu- 
tion, and acquire the characters more or less of the pale or 
grey fibres (fig. 134). 

At certain parts of their course, nerves form j^^^^uses, in 
which they anastomose with each other, and interchange 
fasciculi, as in the case of the brachial and lumbar plexuses. 
The object of such interchange of fibres is, probably, to 
give to each nerve passing ofi" from the plexus, a wider 
connection with the spinal cord than it would have if it 
proceeded to its destination without such communication 
with other nerves. Thus, each nerve by the wideness of 
its connections, is less dependent on the integrity of any 
single portion, whether of nerve-centre or of nerve-trunk, 
from which it may spring. By this means, also, each part 
supplied from a plexus has wider relations with the 
nerve-centres, and more extensive sympathies; and, by 
means of the same arrangement, as Dr. Gull suggests, 
groups of muscles may be associated for combined actions ; 
every member of the group receiving motor filaments from 
the same parts of the nerve-centre. 

The terminations of nerve-fibres are their modes 
of distribution and connection in the nerve-centres, 
and in the parts which they supply : the former are, 
called their central, the latter their 2)g?//?/<^rrt? termina- 
tions. 



PACINIAN BODIES. 4/1 

The peripheral termination of nerve-fibres lias been 
always the subject of considerable discussion and doubt. 
The following appear to be the chief modes of ending of 
nerve-fibres in the parts they supply : — ■ 

I . In fine networks or plexuses ; examples of this are 
found in the distribution of nerves in muscles, and in 
mucous and serous membranes. 2. In special terminal 
organs, called touch-corpuscles (fig. 1 1 3), end-bulbs (fig. 1 14), 
and Pacinian bodies (figs. 1 36, 1 37). 3. In cells; as in the eye 
and internal ear, and some other parts. 4. In free ends ; 
as from the fine plexuses in muscles, according to KoUiker. 
5. In muscles, a peculiar termination of nerves in small 
bodies called motorial end-plates, has been described by 
llouget and others. These small bodies, varying from 
^.oVo- ^^ TTTT ^^ ^^ i^c^ i^ diameter, and placed by different 
observers outside and inside the sarcolemma, are fixed to 
the muscular fibres, one for each, and to them the ex- 
tremity of a minute branch of nerve-fibre is attached. 
These Kttle plates appear to be formed of an expansion of 
the end of a nerve-fibre with a small quantity of con- 
nective tissue. 

The Pacinian bodies or corpuscles (figs. 136 and 1 37), to 
which reference has been just made, are little elongated oval 
bodies, situated on some of the cerebro-spinal and sympa- 
thetic nerves, especially the cutaneous nerves of the hands 
and feet ; and on branches of the large sympathetic plexus 
about the abdominal aorta (Kolliker). They often occur 
also on the nerves of the mesentery, and are especially 
well seen in the mesentery of the cat. They are named 
Pacinian, after their discoverer Pacini. Each corpuscle is 
attached by a narrow pedicle to the nerve on w^hich it is 
situated ; it is formed of several concentric layers of fine 
membrane, with intervening spaces containing fluid; 
through its pedicle passes a single nerve-fibre, which, 
after traversing the several concentric layers and their 
immediate spaces, enters a central cavity, and, gradual!}'' 



47- 



THE NERVOUS SYSTEM. 



losing its dark border, and becoming smaller, terminates 
at or near tbe distal end of the cavity, in a knob-like 
enlargement, or in a bifurcation. The enlargement com- 
monly found at the end of the fibre, is said by Pacini to 
resemble a ganglion-corpuscle; but this observation has 
Fig. 136.* Fig. I37.t 





not been confirmed. The physiological import of these 
bodies seems to be still quite obscure. 

The central termination of nerve-fibres can be better 
considered after the account of the vesicular nerve 
substance. 

* Fig. 136. Extremities of a nerve of the finger with Pacinian cor- 
puscles attached, about the natural size (adapted from Henle and 
Kblliker). 

+ Fig, 137. A magnified view of a single Pacinian corpuscle, shoA\dng 
its laminated structure, and the termination of the nerve-fibre in its 
central cavity (after Bendz). 



STRUCTFEE OF NERVE-CENTRES. 



473 



The vesicular nervous substance contains, as its name 
implies, vesicles or corpuscles, in addition to fibres ; and a 
structure, thus composed of corpuscles and inter-communi- 
cating fibres, usually constitutes a nerve-centre : the chief 
nerve-centres being the grey matter of the brain and 
spinal cord, and the various so-called ganglia. In the 
brain and spinal cord a fine stroma of retiform tissue 
called the neuroglia extends throughout both the fibrous 
Fiff. 138.* FIrj. 139. t 




and vesicular nervous substance, 
and forms a supporting and 
investing frame-work for the 
whole. 

The nerve-corpuscles, which 
give to the ganglia and to 
certain parts of the brain 
and spinal cord the peculiar 
greyish or reddish-grey aspect by which these parts are 
characterized, are large, nucleated cells, filled with a finely 
granular material, some of which is often dark like pig- 




* Fig. 138. Nerve-corpuscles form a ganglion (after Valentin), In 
one a second nucleus is visible. In several the nucleus contains one 
or two nucleoli. 

+ Fig. 139. Stellate or caudate nerve-corpuscles, with tubular pro- 
cesses'issuing from them. Besides being filled with granular material 
continuous with the contents of the processes, the corpuscles contain 
black pigment-matter (after Hannover). 



474 THE NERVOUS SYSTEM. 

ment : tlie nucleus, wliicli is vesicular, contains a nucleolus 
(fig. 138). Besides varying much in sliaj)e, partly in 
consequence of mutual pressure, they present such other 
varieties as make it probable either that there are two 
different kinds, or that, in the stages of their development, 
they pass through very different forms. Some of them are 
small, generally spherical or ovoid, and have a regular 
uninterrupted outline (fig. 138). These simple nerve-cor- 
puscles are most numerous in the sympathetic ganglia; 
Others, which are called caudate or stellate nerve-corpvscles 
(fig. 139), are larger, and have one, two, or more long 
processes issuing from them, the cells being called respec- 
tively M?^^JJoZrtr, bipolar, or multipolar ; which processes often 
divide and subdivide, and appear tubular, and filled with 
the same kind of granular material that is contained within 
the corpuscle. Of these processes some appear to taper to 
a point and terminate at a greater or less distance from 
the corpuscle; some appear to anastomose with similar 
offsets from other corpuscles ; while others are believed to 
become continuous with nerve-fibres, the prolongation from 
the cell by degrees assuming . the characters of the nerve- 
fibre with which it is continuous. 



Functions of Nerve-Fibres. 

The ofiice of the nerves as simple conveyors or con- 
ductors of nervous impressions is of a two-fold kind. 
First, they serve to convey to the nervous centres the 
impressions made upon their peripheral extremities, or 
parts of their course. Secondly, they serve to transmit 
impressions from the brain and other nervous centres to 
the parts to which the nerves are distributed. 

For this two-fold office of the nerves, two distinct sets of 
nerve-fibres are x^rovided, in both the cerebral- spinal and 
sympathetic systems. Those which convey impressions 



FUNCTIONS OF NERVE-FIBRES. 475 

from the periphery to the centre are classed together as 
centripetal or afferent nerves. Those fibres, on th^ other 
hand, wliich are employed to transmit central impulses 
to the periphery are classed as centrifugal or efferent 
nerves. 

Centripetal or afferent nerve-fibres may {a) convey to 
the nerve-centres with which they are connected impres- 
sions which will give rise to sensation (sensitive nerves), or 
(6) they may convey an impression which travels out again 
from the nerve-centre by an efferent nerve-fibre, and pro- 
duces some effect where the latter is distributed, (see 
Section on Bejiex Action), or (c) they may convey an im- 
pression which will produce a restraining or inhihltory 
action in the nerve-centre, (^inhibitory nervea, -p. 13 1). 

Centrifugal or efferent nerves may be (a) for the con- 
veyance of impulses to the voluntary and involuntary 
muscles, (motor nerves,) or (b) they may influence nutrition 
(tropliic nerves), (p. 388,) or (c) they may influence secre- 
tion (sometimes called secretory nerves) (p. 409). 

With this difference in the functions of nerves, there is 
no apparent difference in the structure of the nerve- fibres 
by which it might be explained. Among the cerebro- 
spinal nerves, the fibres of the optic and auditory nerves 
are finer that those of the nerves of common sensation ; 
but, wdth these exceptions, no centripetal fibres can be dis- 
tinguished in their microscopic or general characters from 
those of centrifugal nerves. 

Nerve-fibres possess no power of generating force in 
themselves, or of originating impulses to action : for the 
manifestation of their peculiar endowments they require 
to be stimulated. They possess a certain property of con- 
ducting impressions, a property which has been named 
excitability j but this is never manifested tiU some stimulus 
is applied. Thus, under ordinary circumstances, nerves of 
sensation are stimulated by external objects acting upon 
their extremities j and nerves of motion by the will, or 



476 THE NERVOUS SYSTEM. 

by some force generated in the nervous centres. Uut 
almost all things that can disturb the nerves from their 
passive state act as stimuli, and agents the most dissimilar 
produce the same kind, though not the same degree of 
effect, because that on which they act possesses but one 
kind of excitable force. Thus all stimuli — chemical, 
mechanical, and electric, — when applied to parts endowed 
with sensation, or to sensitive nerves (the connection of the 
latter with the brain and spinal cord being uninjured) pro- 
duce sensations ; and when applied to the nerves of muscles 
excite contractions. Muscular contraction is produced by 
such stimuli as well when the motor nerve is still in con- 
nection with the brain, as when its communication with the 
nervous centres is cut off by dividing it : nerves, therefore, 
have, by virtue of their excitability, the property of exciting 
contractions in muscles to which they are distributed ; and 
the part of the divided motor nerve which is connected 
with the muscle will still retain this power, however much 
we may curtail it. 

Mechanical irritation, when so violent as to injure the 
texture of the primitive nerve-fibres, deprives the centri- 
petal nerves of their power of producing sensations when 
irritation is again applied at a point more distant from the 
brain than the injured spot ; and in the same way, no 
irritation of a motor nerve will excite contraction of the 
muscle to which it is distributed, if the nerve has been 
compressed and bruised between the point of irritation and 
the muscle ; the effect of such an injury being the same as 
that of division. 

The action of nerves is also excited by temperature. Thus, 
when heat is applied to the nerve going to a muscle, or to 
the muscle itself, contractions are produced. These con- 
tractions are very violent when the flame of a candle is 
applied to the nerve, while less elevated degrees of heat, 
— for example, that of a piece of iron merely warmed, — 
do not irritate sufficiently to excite action of the muscles. 



FUNCTIONS OF NERVE-FIBRES. 



477 



The application of cold has the same effect as that of heat. 
The effect of the local action of excessive or long-continued 
cold or heat on the nerves is the same as that of destructive 
mechanical irritation. The sensitive and motor power in 
the part is destroyed, but the other parts of the nerve retain 
their excitability ; and, after the extremity of a divided 
nerve going to a muscle has been burnt, contractions of 
the muscle may be excited by irritating the nerve below 
the burnt part. 

Chemical Stimuli excite the action of both afferent and 
efferent nerves as mechanical irritants do ; provided their 
effect is not so strong as to destroy the structure of the 
nerve to which they are applied. A like manifestation of 
nervous power is produced by electricity and by magnetism. 

Some of these laws regulating the excitability of nerves, 
and their power of manifesting their functions, require 
further notice, with several others which have not yet been 
alluded to. Certain of the laws and conditions of actions 
relate to nerves both centrifugal and centripetal, being de- 
pendent on properties common to all nerve-fibres ; while 
of others, some are peculiar to nerves of motion, some to 
nerves of sensation. 

It is a law of action in aU nerve-fibres, and corresponds 
with the continuity and simplicity of their course, that an 
impression made on any fibre, is simply and uninterruptedly 
transmitted along it, without being imparted or diffused to 
any of the fibres lying near it. In other words, all nerve- 
fibres are mere conductors of impressions. Their adaptation 
to this purpose, is, perhaps, due to the contents of each 
fibre being completely isolated from those of adjacent 
fibres by the membrane or sheath in which each is enclosed, 
and which acts, it may be supposed, just as silk, or other 
non-conductors of electricity do, which, when covering a 
wire, prevent the electric condition of the wire from being 
conducted into the surrounding medium. 



478 THE NERVOUS SYSTEM. 

Nervous force travels along nerve-fibres with considerable 
velocity. Helmholtz and Baxt have estimated the average 
rate of conduction of electrical impressions in human motor 
nerves at 1 1 1 feet per second : this result agreeing very 
closely with that previously obtained by Hirsch. Dr. 
Rutherford's observations agree with those of Von Wittich, 
that the rate of transmission in sensory nerves is about 140 
feet per second. 

Nerve-fibres convey only one kind of impression. Thus, 
a motor fibre conveys only motor impulses, that is, such as 
may produce movements in contractile parts : a sensitive 
fibre transmits none but such as may produce sensation, if 
they are propagated to the brain. Moreover, the fibres of 
a nerve of special sense, as the optic or auditory, convey 
only such impressions as may produce a peculiar sensation, 
e.g., that of light or sound. While the rays of light and 
the sonorous vibrations of the air are without influence on 
the nerves of common sensation, the other stimuli, which 
may produce pain when applied to them, produce, when 
applied to these nerves of special sense, only morbid sensa- 
tions of light, or sound, or taste, according to the nerve 
impressed. 

Of the laws of action peculiar to nerves of sensation and 
of motion respectively, many can be ascertained only by 
experiments on the roots of the nerves. For it is only at 
their origin that the nerves of sensation and of motion are 
distinct ; their filaments, shortly after their departure from 
the nervous centres, are mingled together, so that nearly 
all nerves, except those of the special senses, consist of 
both sensitive and motor filaments, and are hence termed 
mixed nerves. 

Nerves of sensation appear able to convey impressions 
only from the parts in which they are distributed, towards 
the nerve-centre from which they arise, or to which they 
tend. Thus, when a sensitive nerve is divided, and irrita- 



FUNCTIONS OF NERVE-FIBEES. 479 

tion is applied to the end of the proximal portion, i.e., of 
the portion still connected with the nervous centre, sensa- 
tion is perceived, or a reflex action ensues ; but, when the 
end of the distal portion of the divided nerve is irritated, 
no effect appears. 

When an impression is made upon any part of the course 
of a sensitive nerve, the mind may perceive it as if it were 
made not only upon the point to which the stimulus is ap- 
plied, but also upon all the points in which the fibres of the 
irritated nerve are distributed : in other words, the effect 
is the same as if the irritation were applied to the parts 
supplied by the branches of the nerve. When the whole 
trunk of the nerve is irritated, the sensation is felt at all 
the parts which receive branches from it ; but when only 
individual portions of the trunk are irritated, the sensation 
is perceived at those parts only which are supplied by the 
several portions. Thus, if we compress the ulnar nerve 
where it lies at the inner side of the elbow-joint, behind 
the internal condyle, we have the sensation of " pins and 
needles," or of a shock, in the parts to which its fibres are 
distributed, namely, in the palm and back of the hand, 
and in the fifth and ulnar half of the fourth finger. When 
stronger pressure is made, the sensations are felt in the 
fore-arm also ; and if the mode and direction of the pres- 
sure be varied, the sensation is felt by turns in the fourth 
finger, in the fifth, and in the palm of the hand, or in the 
back of the hand, according as different fibres or fasciculi 
of fibres are more pressed upon than others. 

It is in accordance with this law, that when parts are 
deprived of sensibility by compression or division of the 
nerve supplying them, irritation of the portion of the nerve 
connected with the brain still excites sensations which are 
felt as if derived from the parts to which the peripheral 
extremities of the nerve-fibres are distributed. Thus, 
there are cases of paralysis in which the limbs are totally 
insensible to external stimuli, yet are the seat of most 



48o THE NEEVOUS SYSTEM. 

violent pain, resulting apparently from irritation of the 
sound part of the trunk of the nerve still in connection 
with the brain, or from irritation of those parts of the 
nervous centre from which the sensitive nerve or nerves 
which supply the paralysed limbs originate. 

An illustration of the same law is also afforded by the 
cases in which division of a nerve for the cure of neuralgic 
pain is found useless, and in which the pain continues or 
returns, though portions of the nerve be removed. In 
such cases, the disease is probably seated nearer the nervous 
centre than the part at which the division of the nerve is 
made, or it may be in the nervous centre itself. When the 
cause of the neuralgia is seated in the trunk of the nerve — 
for example, of the facial or infra-orbital nerve — division 
of the branches can be of no service ; for the stump remain- 
ing in connection with the brain, and containing all the 
fibres distributed in the branches of the nerve to the skin, 
continues to give rise, when irritated, to the same sensa- 
tions as are felt when the peripheral parts themselves are 
affected. Division of a nerve prevents the possibility of 
external impressions on the cutaneous extremities of its 
fibre being felt ; for these impressions can no longer be 
communicated to the brain : but the same sensations which 
were before produced by external impressions may arise 
^^firom internal causes. In the same way may be explained 
the fact, that when part of a limb has been removed by 

i amputation, the remaining portions of the nerves which 
ramified in it may give rise to sensations which the mind 
refers to the lost part. When the stump and the divided 
nerves are inflamed, or pressed, the patient complains of 
pain felt as if in the part which has been removed. When 
the stump is healed, the sensations which we are accus- 
tomed to have in a sound limb are still felt ; and tingling 
and pains are referred to the parts that are lost, or to par- 
ticular portions of them, as to single toes, to the sole of 

^ the foot, to the dorsum of the foot, etc. 



/ 



FUNCTIOXS OF NERVE-FIBRES. 481 

But (as Volkmann shows) it must not be assumed, as it 
often has been, from these examples, that the mind has no 
power of discriminating the very point in the length of any 
nerve-fibre to which an irritation is applied. Even in the 
instances referred to, the mind perceives the pressure of a 
nerve at the point of pressure, as well as in the seeming 
sensations derived from the extremities of the fibres : and 
in stumps, pain is felt in the stump, as well as, seemingly, 
in the parts removed. It is not quite certain whether those 
sensations are perceived by the nerve-fibres which are on 
their way to be distributed elsewhere, or by the sentient 
extremities of nerves which are themselves distributed to 
the many trunks of the nerves, the nervi nervorum. The 
latter is the more probable supposition. 

The habit of the mind to refer impressions received 
through the sensitive nerves to the parts from which im- 
pressions through those nerves are, or were, commonly 
received, is further exemplified when the relative position 
of the peripheral extremities of sensitive nerves is changed 
artificially, as in the transposition of portions of skin. When 
in the restoration of a nose, a flap of skin is turned down 
from the forehead and made to unite with the stump of the 
nose, the new nose thus formed has, as long as the isthmus 
of skin by which it maintains its original connections re- 
mains undivided, the same sensations as if it were still on 
the forehead; in other words, when the nose is touched, 
the patient feels the impression as if it were made on the 
forehead. When the communication of the nervous fibres 
of the new nose with those of the forehead is cut off by 
division of the isthmus of skin, the sensations are no longer 
referred to the forehead ; the sensibility of the nose is at 
first absent, but is gradually developed. >J 

When, in a part of the body which receives two sensitive 
nerves, one is paralysed, the other may or may not be in- 
adequate to maintaim the sensibility of the entire partj the 
extent to which the sensibility is preserved corresponding 



482 THE NERVOUS SYSTEM. 

probably with the number of the fibres unaffected by the 
paralysis. Thus when the ulnar nerve, which supplies the 
fifth and a part of the fourth finger, is divided, the sensibility 
of those parts is not preserved through the medium of the 
branches which the ulnar derives jfrom the median nerve ; 
but the fourth and fifth fingers are permanently deprived 

y^ of sensibility. On the other hand, there are instances in 
which the trunk of the chief sensitive nerve supplied to a 
part having been divided, the sensibility of the part is 
still preserved by intercommunicating fibres from a neigh- 
bouring nerve-trunk. Thus, a case is related by Mr. 
Savory in which, after excision of a portion of the mus- 
culo- spiral nerve, the sensibility of some of the parts 
supplied by it, although impaired, was not altogether lost, 
probably on account of those fibres jfrom the external 
cutaneous nerve which are mingled with the radial branch 
of the musculo-spiral. One of the uses of a nervous 
plexus (p. 470) is here well illustrated. 

>i Several of the laws of action in motor nerves correspond 
with the foregoing. Thus, the motor influence is propa- 
gated only in the direction of the fibres going to the 
muscles ; by irritation of a motor nerve, contractions are 
excited in all the muscles supplied by the branches given 
off" by the nerve below the point irritated, and in those 
muscles alone : the muscles supplied by the branches 
which come off from the nerve at a higher point than 
that irritated, are never directly excited to contraction. 
No contraction, for instance, is produced in the frontal 
muscle by irritating the branches of the facial nerve that 
ramify upon the face ; because that muscle derives its 
motor nerves from the trunk of the facial previous to these 
branches. So, again, because the isolation of motor nerve- 

■ fibres is as complete as that of sensitive ones, the irritation 
of a part of the fibres of the motor nerve does not affect 
the motor power of the whole trunk, but only that of the 
portion to which the stimulus is applied. And it is from 



FUNCTIONS OF NERVE-CENTEES. 483 

the same fact that, when a motor nerve enters a plexus 
and contributes with other nerves to the formation of a 
nervous trunk proceeding from the plexus, it does not 
impart motor power to the whole of that trunk, but only 
retains it isolated in the fibres which form its continuation 
in the branches of that trunk. 



Functions of Nerve-centres. 

As already observed (p. 473), the term nerve-centre is 
applied to all those parts of the nervous system which 
contain ganglion-corpuscles, or vesicular nerve-substance, 
■i. e., the brain, spinal cord, and the several ganglia which 
belong to the cerebro-spinal and the sympathetic systems. 
Each of these nervous centres has a proper range of 
functions, the extent of which bears a direct proportion to 
'the number of nerve-fibres that connect it with the various 
organs of the body, and with other nervous centres ; but 
they all have certain general properties and modes of action 
-common to the:»n as nervous centres. 

It is generally regarded as the property of nervous 
centres that they originate the impulses by which muscles 
may be excited to action, and by which the several functions 
of organic life may be maintained. Hence, they are often 
called sources or orUjinators of nervous power or force. But 
the instances in which these expressions can be used are 
very few, and, strictly speaking, do not exist at all. The 
brain does not issue any force, except when itself im- 
pressed by some force from within, or stimulated by an 
impression from without; neither without such previous 
impressions do the other nerve-centres produce or issue 
motor impulses. The intestinal ganglia, for example, do 
not give out the nervous force necessary to the contractions 
of the intestines, except when they receive, through their 
centripetal nerves, the stimuli of substances in the intestinal 

I I 2 



484 THE KEEVOUS SYSTEM. 

canal. So, also, the spinal cord ; for a decapitated animal 
lies motionless so long as no irritation is applied to its 
centripetal nerves, though the moment they are touched 
movements ensue. 

The more certain and general office of all the nervous 
centres is that of variously disposing and trans ferring t he 
impressions that reach them through the several centri- 
petal nerve-fibres. In nerve-fibres, as already said, im- 
pressions are only conducted in the simple isolated course 
of the fibre ; in all the nervous centres an impression may 
be not only conducted, but also communicated : in the 
brain alone it may be perceived. 

Conduction in or through nerve-centres may be thus simply 
illustrated. The food in a given portion of the intestines^ 
acting as a stimulus, produces a certain impression on the 
nerves in the mucous membrane, which impression is 
conveyed through them to the adjacent ganglia of the 
sympathetic. In ordinary cases, the consequence of such 
an impression of the ganglia is the movement of the 
muscular coat of that and the adjacent part of the canal. 
But if irritant substances be mingled with the food, the 
sharper stimulus produces a stronger impression, and this 
is conducted through the nearest ganglia to others more 
and more distant; and, from all these, motor impulses 
issuing, excite a wide-extended and more forcible action 
of the intestines. Or even through all the sympathetic 
ganglia, the impression may be further conducted to the 
ganglia of the spinal nerves, and through them to the 
spinal cord, whence may issue motor impulses to the 
abdominal and other muscles, producing cramp. And yet 
further, the same morbid impression may be conducted 
through the spinal cord to the brain, where the mind may 
perceive it. In the opposite direction, mental influence 
may be conducted from the brain through a succession o-f 
nervous centres — the spinal cord and ganglia, and one or 
more ganglia of the sympathetic — to produce the influence 



TR.OSFEREXCE OF IMPRESSIONS. 485 

of the mind on the digestive and other organic functions. 
In short, in all cases in which the mind either has 
cognizance of, or exercises influence on, the processes 
carried on in any part supplied with sympathetic nerves, 
there must be a conduction of impressions through all the 
nervous centres beween the brain and that part. It is 
probable that in this conduction through nervous centres 
the impression is not propagated through uninterrupted 
nerve-fibres, but is conveyed through successive nerve- 
vesicles and connecting nerve-filaments ; and in some 
instances, and when the stimulus is exceedingly powerful, 
the conduction may be effected as quickly as through con- 
tinuous nerve-fibres. 

But instead of, or as well as, being conducted, impres- 
sions made on nervous centres may be communicated from 
the fibres that brought them, to others ; and in this com- 
munication may be either transferred, diffused, or reflected. 

The transference of impressions may be illustrated by the 
pain in the knee, which is a common sign of disease of the 
hip. In this case the impression made by the disease on the 
nerves of the nip-joint is conveyed to the spinal cord; 
there it is transferred to the central ends or connections of 
the nerve-fibres distributed about the knee. Through these 
the transferred impression is conducted to the brain, and 
the mind, referring the sensation to the part from which it 
usually through these fibres receives impressions, feels as 
if the disease and the source of pain were in the knee. At 
the same time that it is transferred, the primary impression 
may be also conducted ; and in this case the pain is felt 
in both the hip and the knee. So, not unfrequently, if 
one touches a small pimple, that may be seated in the 
trunk, a pain will be felt in as small a spot on the arm, or 
some other part of the trunk. And so, in whatever part of 
the respiratory organs an irritation may be seated, the 
impression it produces is transferred to the nerves of the 
larynx ; and then the mind perceives the peculiar sensation 



486 THE NERVOUS SYSTEM. 

of tickling in the glottis, which best, or almost alone, ex- 
cites the act of coughing. Or, again, when the sun's light 
I falls strongly on the eye, a tickling may be felt in the nose, 
I exciting sneezing. In all these cases, the primary impres- 
i sion may be conducted as well as transferred ; and in all it 
j is transferred to a certain set of nerves which generally ap- 
pear to be in some purposive relation with the nerves first 
impressed. 

The diffusion or radiation of imj)ressions is shown when 
an impression received at a nervous centre is diffused to 
many other fibres in the same centre, and produces sensa- 
tions extending far beyond, or in an indefinite area around, 
the part from which the primary impression was derived. 
Hence, as in the former cases, result various kinds of what 
have been denominated sympathetic sensations. Some- 
times such sensations are referred to almost every part of 
the body : as in the shock and tingling of the skin pro- 
duced by some startling noise. Sometimes only the parts 
immediately surrounding the point first irritated partici- 
pate in the effects of the irritation ; thus, the aching of a 
tooth may be accompanied by pain in the adjoining teeth, 
and in all the surrounding parts of the face ; the explana- 
tion of such a case being, that the irritation conveyed to the 
brain by the nerve-fibres of the diseased tooth is radiated 
to the central ends of adjoining fibres, and that the mind 
perceives this secondary impression as if it were derived 
from the peripheral ends of the fibres. Thus, also the 
pain of a calculus in the ureter is diffused far and wide. 

All the preceding examples represent impressions com- 
municated from one sensitive fibre to others of the same 
kind ; or from fibres of special sense to those of common 
sensation. A similar communication of impressions from 
i sensitive to motor fibres, constitutes reflection of impressions, 
\ displays the important functions common to all nervous 
', centres as reflectors, and produces reflex movements. In the 



EEFLECTION OF IMPRESSION. 487 

extent and direction of such communications, also, pheno- 
mena corresponding to those of transference and diffusion 
to sensitive nerves, are observed in the phenomena of 
reflection. For, as in transference, the reflection may take 
place from a certain limited set of sensitive nerves to a 
corresponding and related set of motor nerves ; as when in 
consequence of the impression of light on the retina, the 
iris contracts, but no other muscle moves. Or, as in diffu- 
sion or radiation, the reflection may bring widely-extended 
muscles into action : as when an irritation in the larynx 
brings aU the muscles engaged in expiration into coincident 
movement. 

It will be necessary, hereafter, to consider in detail so 
many of the instances of the reflecting power of the several 
nervous centres, that it may be sufficient here to mention 
only the most general rules of reflex action : — 

1 . For the manifestation of every reflex muscular action, 
three things are necessary ; ( I ), one or more perfect centri- 
petal nerve-fibres, to convey an impression ; (2), a nervous 
centre to which this impression may be conveyed, and by 
which it maj be reflected; (3), one or more centrifugal 
nerve-fibres, upon which this impression may be reflected, 
and by which it may be conducted to the contracting tissue. 
In the absence of any one of these three conditions, a proper 
reflex movement could not take place ; and whenever im- \ 
pressions made by external stimuli on sensitive nerves give i 
rise to motions, these are never the result of the direct | 
reaction of the sensitive and motor fibres of the nerves on 
each other ; in all such cases the impression is conveyed by 
the sensitive fibres to a nervous centre, and is therein com- I 
municated to the motor fibres. \ 

2. All reflex actions are essentially involuntary, and may 
be accomplished independently of the wiU, though most of 
them admit of being modified, controlled, or prevented by 
a voluntary effort. 

3. Reflex actions performed in health have, for the most 



488 THE NERVOUS SYSTEM. 

part, a distinct purpose, and are adapted to secure some 
end desirable for the well-being of the body; but, in 
disease, many of them are irregular and purposeless. As 
an illustration of the first point, may be mentioned move- 
ments of the digestive canal, the respiratory movements, 
and the contraction of the eyelids and the pupil to exclude 
many rays of light, when the retina is exposed to a bright 
glare. These and all other normal reflex acts afford also 
examples of the mode in which the nervous centres combine 
and arrange co-ordinately the actions of the nerve-fibres, 
so that many muscles may act together for the common end. 
Another instance of the same kind is furnished by the 
spasmodic contractions of the glottis on the contact of 
carbonic acid, or any foreign substance, with the internal 
substance of the epiglottis or lamjrx. Examples of the 
purposeless irregular nature of morbid reflex action are 
seen in the convulsive movements of epilepsy, and in the 
spasms of tetanus and hydrophobia. 

4. Reflex muscular acts are often more sustained than 
those produced by the direct stimulus of muscular nerves. 
As Volkmann relates, the irritation of a muscular organ, 
or its motor nerve, produces contraction lasting only so 
long as the irritation continues ; but irritation applied to 
a nervous centre through one of its centripetal nerves, may 
excite reflex and harmonious contractions, which last some 
time after the withdrawal of the stimulus. 

CEREBKO- SPINAL NERVOUS SYSTEM. 

The physiology of the cerebro-spinal nervous system 
includes that of the spinal cord, medulla oblongata, and 
brain, of the several nerves given off from each, and of the 

* Fig. 140. View of the cerebro-spinal axis of the nervous system 
(after Bourgery). — The right half of the cranium and tnmk of the 
body has been removed by a vertical section ; the membranes of the 
brain and spinal marrow have also been removed, and the roots and first 
part of the fifth and ninth cranial, and of all the spinal nerves of the 
right side, have been dissected out and laid separately on the wall of the 



THE CEREBEO-SPIXAL AXIS. 

Fig. 140.* 



489 











^B 









skull and on the several vertebrse opposite to the place of tlieir natural 
exit from the cranio-spinal cavity. 



490 THE NERVOUS SYSTEM. 

ganglia on those nerves. It will be convenient to speak 
first of the spinal cord and its nerves. 

Spinal Cord and its Nerves. 

The spinal cord is a cylindriform column of nerve-sub- 
stance, connected above with the brain through the medium 
of the medulla oblongata, terminating below, about tlie 
lower border of the first lumbar vertebra, in a slender 
filament of grey or vesicular substance, thejilum terminale 
which lies in the midst of the roots of many nerves form- 
ing the Cauda equina. The cord is composed of fibrous 
and vesicular nervous substance, of which the former is 
situated externally, and constitutes its chief portion, while 
the latter occupies its central or axial portion, and is so 
arranged, that on the surface of a transverse section of 
the cord it appears like two somewhat crescentic masses 
connected together by a narrower portion or isthmus (fig. 

141). 

Passing through the centre of this isthmus in a longitu- 
dinal direction is a minute canal, which is continued througli 
the whole length of the cord, and opens above into the 
space at the back of the medulla oblongata and pons 
Varolii, called the fourth ventricle. It is lined by a laj'-er 
of cylindrical ciliated epithelium. 

The spinal cord consists of two exactly symmetrical 
halves united in the middle line by a commissure, but 
separated anteriorly and posteriorly by a vertical fissure ; 
the posterior fissure being deeper, but less wide and dis- 
tinct than the anterior. Each half of the spinal cord is 
marked on the sides (obscurely at the lower part, but dis- 
tinctly above) by two longitudinal furrows, which divide 
it into three portions, columns, or tracts, an anterior, middle 
or lateral, and posterior. From the groove between the 
anterior and lateral columns spring the anterior roots of 
the spinal nerves; and just in front of the groove between 



STRUCTURE OF THE SPINAL CORD. 



491 



the lateral and posterior column arise the posterior roots 
of the same : a pair of roots on each side corresponding to 
each vertebra (fig. 141). 

The fibrous part of the cord contains continuations of the 
innumerable fibres of the spinal nerves issuing from it, or 
entering it ; but it is, probably, not formed of them exclu- 

Flrj. 141.* 




* Fig. 141. Different views of a portion of the spinal cord from the- 
cervical region, with the roots of the nerves slightly enlarged (from 
Quain). In A, the anterior surface of the specimen is shown ; the an- 
teiior nerve-root of its right side being divided ; in b, a view of the 
right side is given ; in c, the upper surface is shown ; in d, the nerve- 
roots and ganglion are shown from heloAV. i. the anterior median 
fissuFe ; 2, posterior median fissure ; 3, anterior lateral depression, over 
which the anterior nerve-roots are seen to spread ; 4, posterior lateral 
gi-oove, into which the posterior roots are seen to sink ; 5, anterior 
roots passing the ganglion ; 5', in A, the anterior root divided ; 6, the 
posterior roots, the fibres of which pass into the ganglion 6' ; 7, the 
united or compound nerve ; 7', the posterior primary branch, seen in 
A and 1) to be derived in part from the anterior and in part from the 
posterior root. 



492 THE XEE.VOUS SYSTEM. 

sively ; nor is it a mere trunk, like a great nerve, through 
which they may pass to the brain. It is, indeed, among 
the most difficult things in structural anatomy to determine 
the course of individual nerve-fibres, or even of fasciculi 
of fibres, through even a short distance of the spinal cord ; 
and it is only by the examination of transverse and longi- 
tudinal sections through the substance of the cord, such as 
those so successfully made by Mr. Lockhart Clarke, that we 
can obtain anything like a correct idea of the direction 
taken by the fibres of the roots of the spinal nerves within 
the cord. From the information afforded by such sections 
it would appear, that of the root-fibres of the nerve which 
enter the' cord, some assume a transverse, others a longi- 
tudinal direction : the fibres of the former pass horizontally 
or obliquely into the substance of the cord, in which many 
of them appear to become continuous with fibres entering 
the cord from other roots ; others pass into the columns of 
the cord, while some perhaps terminate at or near the part 
which they enter : of the fibres of the second set, which 
usually first traverse a portion of the grey substance, some 
pass upwards, and others, at least of the posterior roots, 
turn downwards, but how far they proceed in either direc- 
tion, or in what manner they terminate, are questions still 
undetermined. It is probable that of these latter, many 
constitute longitudinal commissures, connecting different 
segments of the cord with each other ; while others, pro- 
bably, pass directly to the brain. 

The general rule respecting the size of different parts of 
the cord appears to be, that the size of each part bears a 
direct proportion to the siz-^. and number of nerve-roots 
given off from itself, and has but little relation to the size 
or number of those given off below it. Thus the cord is 
very large in the middle and lower part of its cervical 
portion, whence arise the large nerve-roots for the forma- 
tion of the brachial plexuses and the supply of the upper 
extremities, and again enlarges at the lowest part of its 



OEIGIN OF THE SriNAL NEEYES. 493 

dorsal portion and the upper part of its lumbar, at the 
origins of the large nerves which, after forming the lum- 
bar and sacral plexuses, are distributed to the lower 
extremities. The chief cause of the greater size at these 
parts ,of the spinal cord is increase in the quantity of grey 
matter ; for there seems reason to believe that the white 
or fibrous part of the cord becomes gradually and pro- 
gressively larger from below upwards, doubtless from the 
addition of a certain number of upward passing fibres from 
each pair of nerves. 

It may be added, however, that there is no sufficient 
evidence for the supposition that an uninterrupted con- 
tinuity of nerve-fibres is essential to the conduction of 
impressions on the spinal nerves to and from the brain : 
such impressions may be as well transmitted through the 
nerve- vesicles of the cord as by the nerve-fibres ; and the 
experiments of Brown- Sequard, again to be alluded to, 
make it probable that the grey substance of the cord is the 
only channel through which sensitive impressions are con- 
veyed to the brain. 

The Nerves of the Spinal Cord consist of thirty-one pairs, 
issuing from the sides of the whole length of the cord, their 
number corresponding with the intervertebral foramina 
through which they pass. Each nerve arises by two roots, 
an anterior and posterior, the latter being the larger. The 
roots emerge through separate apertures of the sheath 
of dura mater surrounding the cord ; and directly after 
their emergence, where the roots lie in the intervertebral 
foramen, a ganglion is found on the posterior root. The 
anterior root lies in contact with the anterior surface of 
the ganglion, but none of its fibres intermingle with those 
in the ganglion. But immediately beyond the ganglion 
the two roots coalesce, and by the mingling of their fibres 
form a compound or mixed spinal nerve, which, after 
issuing from the intervertebral canal, divides into an 



494 THE NERVOUS SYSTEM. 

anterior and posterior branch, each containing fibres from 
both the roots (fig. 141). 

According to KoUiker the posterior root-fibres of the 
cord enter into no connection with the nerve-corpuscles in 
the ganglion, but pass directly through, in one or more 
bundles, which are collected into a trunk beyond the gan- 
glion, and then join the motor root. From most, if not aU, 
of the ganglionic corpuscles, one or two, rarely more, 
nerve-fibres arise and pass out of the ganglion, in a peri- 
pheral direction, in company with the posterior root-fibres 
of the cord. Each spinal ganglion, therefore, is to be 
regarded as a source of new nerve-fibres, which Kolliker 
names ganglionic fibres. The destination of these fibres is 
not yet determined : probably they pass especially into the 
vascular branches of the nerves which they accompany. 

The anterior root of each spinal nerve arises by nume- 
rous separate and converging fasciculi from the anterior 
column of the cord ; the posterior root by more numerous 
parallel fasciculi, from the posterior column, or, rather, 
from the posterior part of the lateral column ; for if a 
fissure be directed inwards from the groove between the 
middle and posterior columns, the posterior roots will 
remain attached to the former. The anterior roots of each 
spinal nerve consist exclusively of motor fibres; the 
posterior as exclusively of sensitive fibres. For the know- 
ledge of this important fact, and much of the consequent 
progress of the physiology of the nervous system, science 
is indebted to Sir Charles Bell. The fact is proved in 
various ways. Division of the anterior roots of one or 
more nerves is followed by complete loss of motion in the 
parts supplied by the fibres of such roots ; but the sensa- 
tion of the same parts remains perfect. Division of the 
posterior roots destroys the sensibility of the parts supplied 
by their fibres, while the power of motion continues unim- 
paired. Moreover, irritation of the ends of the distal 
portions of the divided anterior roots of a nerve excites 



• FUNCTIONS OF THE SPINAL COED. 495 

muscular movements , irritation of the ends of the proximal 
portions, which are still in connection with the cord, is 
followed by no effect. Irritation of the distal portions of 
the divided posterior roots, on the other hand, produces no 
muscular movements and no manifestation of pain ; for, as 
already stated, sensitive nerves convey impressions only 
towards the nervous centres : but irritation of the proximal 
portions of these roots elicit signs of intense suffering. 
Occasionally, under this last irritation, muscular move- 
ments also ensue ; but these are either voluntary, or the 
result of the irritation being reflected from the sensitive to 
the motor fibres. Occasionally, too, irritation of the distal 
ends of divided anterior roots elicits signs of pain, as weU 
as producing muscular movements : the pain thus excited 
is probably the result of cramp (Brown-Sequard). 

As an example of the experiments of which the preced- 
ing paragraph gives a summary account, this may be 
mentioned : If in a frog the three posterior roots of the 
nerves going to the hinder extremity be divided on the left 
side, and the three anterior roots of the corresponding 
nerves on the right side, the left extremity wiU be deprived 
of sensation, the right of motion. If the foot of the right 
leg, which is still endowed with sensation but not with the 
power of motion, be cut off, the fi'og will give evidence of 
feeling pain by movements of all parts of the body except 
the right leg itself, in which he feels the pain. If, on the 
contrary, the foot of the left leg, which has the power 
of motion, but is deprived of sensation, is cut off, the frog 
does not feel it, and no movement follows, except the 
twitching of the muscles irritated by cutting them or their 
tendons. 

Functions of the Spinal Cord. 

The spinal cord manifests all the properties already 
assigned to nerve centres (see p. 483). 

I . It is capable of conducting impressions, or states of 



496 THE NERVOUS SYSTEM. 

nervous excitement. Througli it the impressions made 
upon the peripheral extremities or other parts of the spinal 
sensitive nerves are conducted to the brain, where alone 
they can be perceived by the mind. Through it, also, the 
stimulus of the will, applied to the brain, is capable of 
exciting the action of the muscles supplied from it with 
motor nerves. And for all these conductions of impressions 
to and fro between the brain and the spinal nerves,' the 
perfect state of the cord is necessary ; for when any part 
of it is destroyed, and its communication with the brain is 
interrupted, impressions on the sensitive nerves given off 
from it below the seat of injury, cease to be propagated to 
the brain, and the mind loses the power of voluntarily 
exciting the motor nerves proceeding from the portion of 
cord isolated from the brain. 

Illustrations of this are furnished by various examples 
of paralysis, but by none better than by the common para- 
plegia, or loss of sensation and voluntary motion in the 
lower part of the body, in consequence of destructive 
disease or injury of a portion, including the whole thick- 
ness, of the spinal cord. Such lesions destroy the com- 
munication between the brain and all parts of the spinal 
cord below the seat of injury, and consequently cut off' 
from their connection with the mind the various organs 
supplied with nerves issuing from those parts of the cord. 
But if this lower portion of the cord preserves its integrity, 
the various parts of the body supplied with nerves from it, 
though cut off from the brain, will nevertheless be subject 
to the influence of the cord, and, as presently to be shown, 
will indicate its other powers as a nervous centre. 

From what has been already said, it will appear probable 
that the conduction of impressions along the cord is effected 
(at least, for the most part) through the grey substance, 
i. e., through the nerve-corpuscles and fflaments connecting 
them. But there is reason to believe that all parts of the 
cord are not alike able to conduct all impressions; and 



FUNCTIONS OF THE SPINAL CORD. 



497 



that, rather, as there are separate nerve-fibres for motor 
and for sensitive impressions, so in the cord, separate and 
determinate parts serve to conduct always the same kind 
of impression. 

The important and philosophical labours of Dr. Brown- 




* The above diagi-am (after Brown-Sequard) represents the decus- 
sation of the conductors for voluntary movements, and those for 
sensation : a r, anterior roots and their continuations in the spinal 
cord, and decussation at the lower part of the medulla oblongata, mo; 
p r, the posterior roots and their continuation and decussation in the 
spinal cord ; g g, the ganglions of the roots. The arrows indicate the 
direction of the nervous action ; r, the right side ; I, the left side. 
I, 2, 3, indicate places of alteration in a lateral half of the spino- 
cerebral axis, to show the influence on the two kinds of conductors, 
resulting from section of the cord at any one of these three places. 

K 



498 THE NERVOUS SYSTEM. 

Sequard have cast mucli new light on all relating to 
the functions of the spinal cord. It is not possible to 
do justice to these investigations in any summary, how- 
ever lengthy and complete : the whole series (delivered 
in lectures at the CoUege of Surgeons) must be 
read and studied. An attempt will be made here to 
point out only the principal conclusions deducible from 
them. 

a. Sensitive impressions, conveyed to the spinal cord by 
root-fibres of the posterior nerves are not conducted to the 
brain by the posterior columns of the cord, as hitherto has 
been generally supposed, but pass through them into the 
central grey substance, by which they are transmitted to 
the brain (fig. 142). 

h. The impressions thus conveyed to the grey substance 
do not pass up to the brain along that half of the cord 
corresponding to the side from which they have been 
received, but, almost immediately after entering the cord, 
cross over to the other side, and along it are transmitted 
to the brain. There is thus, in the cord itself, a complete 
decussation of sensitive impressions brought to it ; so that 
division or disease of one posterior half of the cord is 
followed by lost sensation, not in parts on the correspond- 
ing, but in those of the opposite side of the body. 

c. The various sensations of touch, pain, temperature, 
and muscular contraction, are probably conducted along 
separate and distinct sets of fibres. All, however, with 
the exception of the last named, undergo decussation in the 
spinal cord, and along it are transmitted to the brain by 
the grey matter. 

d. The posterior columns of tlie cord appear to have a 
great share in reflex movements, and this is the principal 
cause of the peculiar kind of paralysis so often observed in 
disease of these columns. 

e. Impulses of the wiU, leading to voluntary contractions 
of muscles, appear to be transmitted principally along the 



CONDITION OF THE SPIXAL COED. 



499 



anterior columns, and the contiguous grey matter of the 
cord. 

/. Decussation of motor impulses occurs, not in the 
spinal cord, as is the case with sensitive impressions, but, 
as hitherto admitted, at the interior part of the medulla 
oblongata. This decussation, however, does not take place, 
as generally supposed, all along the median line, at the 
base of the encephalon, but only at that portion of the 
, anterior pyramids, which is continuous with the lateral 
columns of the cord. Hence, the mandates of the will, 
having made their decussation, first enter the cord by the 
lateral tracts and adjoining grey matter, and then pass to 
the anterior columns and to the grey matter associated 
with them. Accordingly, division of the anterior pyramids, 
at the point of decussation, is followed by paralysis of 
motion in all parts below; while division of the olivary 
bodies, which constitute the true continuations of the 
anterior columns of the cord, appears to produce very 
little paralysis. Disease or division of any part of the 
cerebro-spinal axis above the seat of decussation is followed, 
as well-known, by impaired or lost power of motion on 
the opposite side of the body; while a like injury inflicted 
helow this part, induces similar paralysis on the corre- 
sponding side. 

2. In the second place, the spinal cord as a nerve- 
centre, or rather as an aggregate of many nervous centres, 
has the power of communicating impressions in the several 
ways already mentioned (p. 485)- 

Examples of the transference and radiation of impressions 
in the cord have been given ; and that the transference at 
least takes place in the cord, and not in the brain, is nearly 
proved by the case of pain felt in the knee and not in the 
hip, in diseases of the hip ; of pain felt in the urethra or 
glans penis, and not in the bladder, in calculus ; for, if 
both the primary and the secondary or transferred impres- 
sions were in the brain, both should be always felt. Of 

K K 2 



500 THE Is^EEYOUS SYSTEM. 

radiations of impressions, there are, perhaps, no means 
of deciding whether they take place in the spinal cord or 
in the brain ; but the analogy of the cases of transference 
makes it probable that the communication is, in this also, 
effected in the cord. 

The power, as a nerve-centre, of communicating im- 
pressions from sensitive to motor, or, more strictly, from 
centripetal to centrifugal nerve-fibres, is what is usually 
discussed as the refiex function of the spinal cord. Its 
general mode of action, its general though incomplete 
independence of consciousness and of the will, and the- 
conditions necessary for its perfection, have been already 
stated. These points, and the extent to which the power 
operates in the production of the natural refiex movements- 
of the body, have now to be further illustrated. They 
will be described in terms adapted to the general rules of 
reflection of impressions in nervous centres, avoiding all 
such terms as might seem to imply that the power of the 
spinal cord in reflecting, is different in kind from that of 
all other nervous centres. 

The occurrence of movements under the influence of the 
spinal cord, and independent of the will, is well exemplified 
in the acts of swallowing, in which a portion of food 
carried by voluntary efforts into the fauces, is conveyed by 
successive involuntary contractions of the constrictors of 
the pharynx and muscular walls of the oesophagus into 
the stomach. These contractions are excited by the stimu- 
lus of the food on the centripetal nerves of the pharynx 
and oesophagus being first conducted to the spinal cord 
and medulla oblongata, and thence reflected through the 
motor nerves of these parts. All these movements of the 
pharynx and oesophagus are involuntary; the will cannot 
arrest them or modify them ; and though the mind has a 
certain consciousness of the food passing, which becomes 
less as the food passes further, yet that this is not neces- 
sary to the act of deglutition, is shown by its occurring 



REFLEX FUNCTION OF THE SPINAL CORD 501 

when the influence of the mind is completely removed ; as 
when food is introduced into the fauces or pharynx during 
a state of complete coma, or in a brainless animal. 

So also, for example, under the influence of the spinal 
cord, the involuntary and unfelt muscular contraction of 
the sphincter aiii is maintained when the mind is com- 
pletely inactive, as in deep sleep, but ceases when the 
lower part of the cord is destroyed, and cannot be main- 
tained by the will. 

The independence of the mind manifested by the reflect- 
ing power of the cord, is further shown in the perfect 
occurrence of the reflex movements when the spinal cord 
and the brain are disconnected, as in decapitated animals, 
and in cases of injuries or diseases so affecting the spinal 
€ord as to divide or disorganize its whole thickness at any 
part whose perfection is not essential to life. Thus, when 
the head of a lizard is cut off, the trunk remains .standing 
on the feet, and the body writhes when the skin is irritated. 
If the animal be cut in two, the lower portion can be ex- 
cited to motion as well as the upper portion : the tail may 
be divided into several segments, and each segment, in 
which any portion of spinal cord is contained, contracts on 
the slightest touch ; even the extremity of the tail moves 
as before, as soon as it is touched. All the portions of the 
animal in which these movements can be excited, contain 
some part of the spinal cord ; and it is evidently the cause 
of the motions excited by touching the surface ; for they 
cannot be excited in parts of the animal, however large, if 
no part of the cord is contained in them. Mechanical irri- 
tation of the skin excites not the slightest motion in the 
leg when it is separated from the body ; yet the extremity 
of the tail moves as soon as it is touched. The same power 
of the spinal cord in reflecting impressions will cause an 
eel, or a frog, or any other cold-blooded animal, to move 
along after it is deprived of its head, and when, however 
much the movements may indicate purpose, it is not 



502 THE XERVOUS SYSTEM. 

probable that consciousness or will has any share in 
them. And so, in the human subject, or any warm- 
blooded animal, when the cord is completely divided 
across, or so diseased at some part that the influence 
of the mind cannot be conveyed to the parts below it, 
the irritation of any part of the surface supplied by 
nerves given off from the cord below the seat of injur}^, 
is commonly followed by spasmodic aijd irregular reflex 
movements, even though in the healthy state of the cord, 
such involuntary movements could not be excited when 
the attention of the mind was directed to the irritating 
cause. 

In the fact last mentioned, is an illustration of an impor- 
tant difference between the warm-blooded and the lower 
animals, in regard to the reflecting power of the spinal cord 
(or its homologue in the Invertebrata), and the share which 
it and the brain have, respectively, in determining the 
several natural movements of the body. When, for ex- 
ample, a frog's head is cut off, the limbs remain in, or 
assume, a natural position ; resume it when disturbed ; and 
when the abdomen or back is irritated, the feet are moved 
with the manifest purpose of pushing away the irritation. 
It is as if the mind of the animal were still engaged in 
the acts.'*' But, in division of the human spinal cord, the 
lower extremities fall into any position that their weight 
and the resistance of surrounding objects combine to give 
them ; if the body is irritated, they do not move towards 
the irritation ; and if themselves are touched, the conse- 
quent movements are disorderly and purposeless. Now, if 

* The evident adaptation and purpose in the movements of the cold- 
l)looded animals, have led some to think that they must be conscious 
and capable of will without their brains. But purposive movements, 
are no proof of consciousness or will in the creature manifesting them. 
The movements of the limbs of headless frogs are not more purposive 
than the movements' of our own respiratory muscles are ; in which we 
know that neither will nor consciousness is at all times concerned. 



REFLEX FU:N^CTI0N OF THE SPII^AL CORD. 503 

we are justified by analogy in assuming that the will of 
the frog cannot act more than the will of man, through 
the spinal cord separated from, the brain, then it must be 
admitted that many more of the natural and purposive 
movements of the body can be performed under the sole 
influence of the cord in the frog than in man ; and what 
is true in the instance of these two species, is generally 
true also of the whole class of cold-blooded, as distinguished 
from warm-blooded, animals. It may not, indeed, be 
assumed that the acts of standing, leaping, and other 
movements, which decapitated cold-blooded animals can 
perform, are also always, in the entire and healthy state, 
performed involuntarily, and under the sole influence of 
the cord ; but it is probable that such acts may be, and 
commonly are, so performed, the higher nerve-centres 
of the animal having only the same kind of influence in 
modifying and directing them, that those of man have in 
modifying and directing the movements of the respiratory 
muscles. 

The fact that such movements as are produced by irri- 
tating the ski'-i of the lower extremities in the human 
subject, after division or disorganization of a part of the 
spinal cord, do not follow the same irritation when the 
mind is active and connected with the cord through the 
brain, is, probably, due to the mind ordinarily perceiving 
the irritation and instantly controlling the muscles of the 
irritated and other parts ; for, even when the cord is per- 
fect, such involuntary movements will often follow irritation^ 
if it be applied when the mind is wholly occupied. When, 
for example, one is anxiously thinking, even slight stimuli 
will produce involuntary and reflex movements. So, also, 
during sleep, such reflex movements may be observed when 
the skin is touched or tickled ; for example, when one touches 
with the finger the palm of the hand of a sleeping child, 
the finger is grasped — the impression on the skin of the 
palm producing a reflex movement of the muscles which 



504 



THE NERVOUS SYSTEM. 



close the hand. But when the child is awake, no such 
effect is produced by a similar touch. 

On the whole, it may, from these and like facts, be con- 
cluded that the proper reflex acts, performed under the 
influence of the reflecting power of the spinal cord, are 
essentially independent of the brain, and may be performed 
perfectly when the brain is separated from the cord : -^ that 
these include a much larger number of the natural and 
purposive movements of the lower animals than of the 
warm-blooded animals and man : and that over nearly all 
of them the mind may exercise, through the brain, some 
control; determining, directing, hindering, or modifying 
them, either by direct action or by its power over associated 
muscles. 

In this fact, that the reflex movements from the cord 
may be perfectly performed without the intervention of 
consciousness or will, yet are amenable to the control of 
the will, we may see their admirable adaptation to the 
well-being of the body. Thus, for example, the respiratory 
movements may be performed while the mind is, in other 
things, fully occupied, or in sleep powerless; yet in an 
emergency, the mind can direct and strengthen them : and 
it can adapt them to the several acts of speech, effort, etc. 
Being, for ordinary purposes, independent of the will and 
consciousness, they are performed perfectly, without expe- 
rience or education of the mind ; yet they may be employed 
for other and extraordinary uses when the mind wills, and 
so far as it acquires power over them. Being commonly 
independent of the brain, their constant continuance does 
not produce weariness ; for it is only in the brain that it or 
any other sensation can be perceived. 

The subjection of the muscles to both the spinal cord 

* Reflex movements, occurring quite independently of sensation, are 
generally called excito-niotor j those which are guided or accompanied 
"by sensation, but not to the extent of a distinct perception or intel- 
lectual process, are termed setisori-motor. 



EEFLEX FUNCTION OF THE SPINAL COED. 505 

and the brain, makes it difficult to determine in man what 
movements or what share in any of them can be assigned 
to the reflecting power of the cord. The fact that after 
division or disorganization of a part of the cord, move- 
ments, and even forcible though purposeless ones, are pro- 
duced in the lower limbs when the skin is irritated, proves 
that the spinal cord can reflect a stimulus to the action of 
the muscles that are, naturally, most under the control of 
the wiU ; and it is, therefore, not improbable that, for even 
the involuntary action of those muscles, when the cord is per- 
fect, it may supply the nervous stimulus, and the wiU the 
direction. As instances in which it supplies both stimulus 
and direction, that is, both excites and determines the com- 
bination of muscles, may be mentioned the acts of the abdo- 
minal muscles in vomiting and voiding the contents of the 
bladder and rectum ; in both of which, though, after the 
period of infancy, the mind may have the power of post- 
poning or modifying the act, there are all the evidences of 
reflex action; namely, the necessary precedence of a sti- 
mulus, the independence of the will, and, sometimes of 
consciousness, the combination of many muscles, the per- 
fection of the act without the help of education or experi- 
ence, and its failure or imperfection in disease of the lower 
part of the cord. The emission of semen is equally a reflex 
act governed by the spinal cord : the irritation of the glans 
penis conducted to the spinal cord, and thence reflected, 
excites the successive and co-ordinate contractions of the 
muscular fibres of the vasa deferentia and vesiculae semi- 
nales, and of the accelerator urina3 and other muscles of 
the urethra ; and a forcible expulsion of semen takes place, 
over which the mind has little or no control, and which, in 
cases of paraplegia, may be unfelt. The erection of the 
peuis, also, as already explained (p. 185), appears to be in 
part the result of a reflex contraction of the muscles by 
which the veins returning the blood from the penis are 
compressed. Irritation of the vagina in sexual intercourse 



506 THE KERVOUS SYSTEM. 

appears also to be propagated to the spinal cord, and thence 
reflected to the motor nerves supplying the Fallopian tubes. 
The involuntary action of the uterus in expelling its con- 
tents during parturition, is also of a purety reflex kind, 
dependent in- part upon the spinal cord, though in part 
also upon the sympathetic system : its independence of the 
brain being proved by cases of delivery in paraplegic 
women, and now more abundantly shown in the use of 
chloroform. 

Besides these acts regularly performed under the influ- 
ence of the reflecting power of the spinal cord, others are 
manifested in accidents, such as the movement of the limbs 
and other parts to guai'd the body against the effects of 
sudden danger. When, for example, a limb is pricked or 
struck, it is instantly and involuntarily withdrawn from the 
instrument of injuiy ; and the same preservative tendency 
of the reflex power of the cord is shown in the outstretched 
arms when falling forwards, and their reversed position 
when falling backwards ; the action, although apparently 
voluntary, being really, in most cases, only an instance of 
reflex action. 

To these instances of spinal reflex action, some add yet 
many more, including nearly all the acts which seem to be 
performed unconsciously, such as those of walking, running, 
writing, and the like : for these are really involuntary 
acts. It is true that at their first performances they are 
voluntary, that they require education for their perfection, 
and are at all times so constantly performed in obedience 
to a mandate of the will, that it is difficult to believe in 
their essentially involuntary nature. But the will really 
has only a controlling power over their performance ; it can 
hasten or stay them, but it has little or nothing to do with 
the actual carrying out of the effect. And this is proved 
by the circumstance that these acts can be performed with 
complete mental abstraction : and, more than this, that the 
endeavour to carry them out entirely by the exercise of the 



L 



EEFLEX FUNCTION OF THE SPINAL COED. 507 

will is not onlj^ not beneficial, but positively interferes with, 
their harmonious and perfect performance. Anyone may 
convince himself of this fact by trying to take each step as 
a voluntary act in walking down stairs, or to form each 
letter or word in writing by a distinct exercise of the will. 

These actions, however, will be again referred to, when 
treating of their possible connection with the functions of 
the so-called sensory ganglia (p. 523). 

The phenomena of spinal reflex actions in mail are much, 
more striking and unmixed in cases of disease. In some of 
these, the effect of a morbid irritation, or a morbid irri- 
tability of the cord, is very simple ; as when the local 
irritation of sensitive fibres, being propagated to the 
spinal cord, excites merely local spasms, — spasms, namely, 
of those muscles, the motor fibres of which arise from the 
same part of the spinal cord as the sensitive fibres that are 
irritated. Of such a case we have instances in the invol- 
untary spasmodic contraction of muscles in the immediate 
neighbourhood of inflamed joints; and numerous other 
examples of a like kind might be quoted. 

In other instances, in which we must assume that the 
cord is morbidly more irritable, i.e., apt to issue more 
nervous force than is proportionate to the stimulus applied 
to it, a slight impression on a sensitive nerve produces ex- 
tensive reflex movements. This appears to be the condition 
in tetanus, in which a slight touch on the skin may throw 
the whole body into convulsion. A similar state is induced 
by the introduction of strychnia, and, in frogs, of opium, 
into the blood ; and numerous experiments on frogs thus 
made tetanic, have shown that the tetanus is wholly uncon- 
nected with the brain, and depends on the state induced in 
the spinal cord. 

It may seem to have been implied that the spinal cord, as 
a single nervous centre, reflects alike from aU parts all the 
impressions conducted to it. But it is more probable that 



5o8 THE NEHYOUS SYSTEM. 

it should be regarded as a collection of nervous centres 
united in a continuous column. This is made probable by 
the fact that segments of the cord may act as distinct ner- 
vous centres, and excite motions in the parts supplied with 
nerves given off from them ; as well as by the analogy of 
certain cases in which the muscular movements of single 
organs are under the control of certain circumscribed por- 
tions of the cord. Thus Volkmann has shown that the 
rhythmical movements of the anterior pair of lymphatic 
hearts in the frog depend upon nervous influence derived 
from the portion of spinal cord corresponding to the third 
vertebra, and those of the posterior pair on influence sup- 
plied by the portion of cord opposite the eighth vertebra. 
The movements of the heart continue, though the whole of 
the cord, except the above portions, be destroyed ; but on 
the instant of destroying either of these portions, though 
all the rest of the cord be untouched, the movements of 
the corresponding hearts cease. What appears to be thus 
' proved in regard to two portions of the cord, may be in- 
ferred to prevail in other portions also ; and the inference 
is reconcilable with most of the facts known concerning 
the physiology and comparative anatomy of the cord. 

The influence of the spinal cord on the sphincter ani has 
been already mentioned (p. 501). It maintains this muscle 
in permanent contraction, so that, except in the act of defeca- 
tion, the orifice of the anus is always closed. This influence 
of the cord resembles its common reflex action in being in- 
voluntary, although the will can act on the muscle to make 
it contract more or to permit its dilatation, and in that the 
constant action of the muscle is not felt, nor diminished in 
sleep, nor productive of fatigue. But the act is different 
from ordinary reflex acts in being nearly constant. In 
this respect it resembles that condition of muscles which 
has been called tone,^ or passive contraction ; in a state in 

* This kind of tone must be distinguished from that mere firmness 



STEUCTUEE OF THE MEDULLA OBLOXGATA. 



509 



wliich they always appear to be when not active in health, 
and in which, though called inactive, they appear to be in 
slight contraction, and certainly are not relaxed, as they 
are long after death, or when the spinal cord is destroyed. 
This tone of all the muscles of the trunk and limbs seems 
to depend on the spinal cord, as the contraction of the 
sphincter ani does. If an animal be IdUed by injury or 
removal of the brain, the tone of the muscles may be felt, 
and the limbs feel firm as during sleep ; but if the spinal 
cord be destroyed, the sphincter ani relaxes, and all the 
muscles feel loose, and flabby, and atonic, and remain so- 
till the rigor mortis commences. 

THE MEDULLA OBLONGATA. 

Its Structure. 

The medulla oblongata is a mass of grey and white 
nervous substance partly contained within the cavity of the 
cranium, — forming a portion of the cephalic prolongation 
of the spinal cord and connecting it with the brain. The 
grey substance which ifc contains is situated in the interior, 
and variously divided into masses and laminae by the white 
or fibrous substance which is arranged partly in external 
columns, and partly in fasciculi traversing the central grey 
matter. The medulla oblongata is larger than any part of 
the spinal cord. Its columns are pyriform, enlarging as 
they proceed towards the brain, and are continuous with 
those of the spinal cord. 

Each half of the medulla, therefore, may be divided into 
three columns or tracts of fibres, continuous with the three 



nnd tension wliicli it is customary to ascribe, under the name of tone, 
to all tissiies that feel robust and not flabby, as well as to muscles. 
The tone pecidiar to muscles has in it a degi-ee of vital contraction : 
that of other tissues is only due to their being well nourished, and 
therefore compact and tense. 



5IO 



THE NERVOUS SYSTEM. 



tracts of wliicli eacli lialf of the spinal cord is made up. 
The columns are more prominent than those of the spinal 
cord, and separated from each other by deeper grooves. The 
anterior, continuous with the anterior columns of the cord, 
are called the anterior jpyramids; the posterior, continuous 
with the posterior columns of the cord, are called the restiform 

143.* ^io- i44.t 




* Fig. 143. View of the anterior surface of tlie pons Varolii, and 
medulla oblongata, a, a, anterior pyramids ; b, their decussation ; c, c, 
olivary bodies ; d, d, restiform bodies ; e, arciform fibres ; /, fibres 
described by Solly as passing from the anterior column of the cord to 
the cerebellimi ; g, anterior column of the spinal cord ; h, lateral 
column ; 2h pons Varolii ; i, its upper fibres ; 5, 5, roots of the fifth 
pair of nerves. 

t Fig. 144. View of the posterior surface of the pons Varolii, cor- 
pora quadrigemina, and medulla oblongata. The peduncles of the, 
cerebellum are cut short at the side, a, a, the upper pair of cor- 
l)ora quadrigemina ; 5, h, the loAver ; /, /, supeiior peduncles of the 
cerebellum ; c, eminence connected with the nucleus of the h}Tioglossal 
nerve ; e, that of the glosso-pharyngeal nerve ; i, that of the vagu.s 
nerve ; d, d, restiform bodies ; ^;, ]j, posterior pyramids ; v, v, groove 
in the middle of the fourth ventricle, ending below in the calamus 
scrix)torius ; 7, 7, roots of the auditory nerves. 



STEUCTURE OF THE MEDULLA OBLONGATA. 5 1 1 

bodies ; and tlie lateral, continuous witli the lateral columns 
of tlie cord, are named simply from tlieir position. On the 
fibres of the lateral column of each side, near its upper 
part, is a small oval mass containing grey matter, and 
named the olivary body ; and at the posterior part of the 
restiform column, immediately on each side of the posterior 
median groove, a small tract is marked off by a slight 
groove from the remainder of the restiform body, and called 
the posterior pyramid. The restiform columns, instead of 
remaining parallel with each other throughout the whole 
of the medulla oblongata, diverge near its upper part, 
and by thus diverging, lay open, so to speak, a space called 
the fourth ventricle, the floor of which is formed by the 
grey matter of the interior of the meduUa, by this diverg- 
ence exposed. 

On separating the anterior pyramids, and looking into 
the groove between them, some decussating fibres can be 
plainly seen. 

Distribution of the Fibres of the MeduUa Oblongata. 

The anterior pyramid of each side, although mainly com- 
posed of continuations of the fibres of the anterior columns 
of the spinal cord, receives fibres from the lateral columns, 
both of its own and the opposite side ; the latter fibres 
forming almost entirely those decussating strands before 
mentioned, which are seen in the groove between the 
-anterior pyramids. 

Thus composed, the anterior pyramidal fibres proceed- 
ing onwards to the brain are distributed in the following 
manner: — I. The greater part pass on through the pons 
to the cerebrum.'" A portion of the fibres, however, run- 



* The expressions '•continuous fibres," and the like, appear to he 
usually understood as meaning that certain primitive nerve-fibres pass 
without interruption from one part to another. But such continuity 
of primitive fibres through long distances in the nervous centres is 



512 THE NERVOUS SYSTEM. 

ning apart from tlie others, joins some fibres from the 
olivary body, and unites with them to form what is called 
the olivary fasciculus or fillet. 2. A small tract of fibres 
proceeds to the cerebellum. 

The lateral column on each side of the medulla, in pro- 
ceeding upwards, divides into three parts, outer, inner, 
and middle, which are thus disposed of: — I. The outer 
fibres go with the restiform tract to the cerebellum. 2. The 
middle decussate across the middle line with their fellows, 
and form a part of the anterior pyramid of the opposite 
side. 3. The iwner pass on to the cerebrum along the floor 
\ of the fourth ventricle, on each side, under the name of the 
\ fasciculus teres. 

The fibres of the restiform body receive some small con- 
tributions from both the lateral and anterior columns of 
the medulla, and proceed chiefly to the cerebellum, but 
that small part behind, called posterior pyramid, is con- 
tinued on with the fasciculus teres of each side along the 
floor of the fourth ventricle to the cerebrum. 

As in structure, so also in the general endowments of 
their several parts, there is, probably, the closest analogy 
between the medulla oblongata and the spinal cord. The 
difference between them in size and form appears due, 
chiefly, first, to the divergence, enlargement, and decussa- 
tion of the several columns, as they pass to be connected 
with the cerebellum or the cerebrum ; and, secondly, to the 
insertion of new quantities of grey matter in the olivary 
bodies and other parts, in adaptation to the higher office 



very far from proved. The apparent continuity of fasciculi (wliich is 
all that dissection can yet trace) is explicable on the supposition that 
many comparatively short fibres He parallel, with the ends of each 
inlaid among many others. In such a case, there would be an apparent 
continuity of fibres ; just as there is, for example, when one untwists 
and picks out a long cord of silk or wool, in which each fibre is short, 
and yet each fasciculus appears to be continued through the whole 
cord. 



FUNCTIONS t)F THE MEDULLA OBLONGATA. 513 

and wider range of influence which the medulla oblongata 
as a nervous centre exercises. 



Functions of the Medulla Oblongata. 

In its functions the medulla oblongata differs from the 
spinal cord chiefly in the importance and extent of the 
actions that it governs. Like the cord, it may be regarded 
first, as conducting impressions, in which office it has a 
wider extent of function than any other part of the nervous 
system, since it is obvious that all impressions passing to 
and fro between the brain and the spinal cord and all 
nerves arising below the pons, must be transmitted through 
it. The decussation of part of the fibres of the anterior 1 
pyramids of the medulla oblongata explains the pheno- 
mena of cross-paralysis, as it is termed, i. e., of the loss of 
motion in cerebral apoplexy, being always onT^the side 
opposite to that on which the effusion of blood has taken ^ 
place. Looking only to the anatomy of the medulla | 
oblongata, it was not possible to explain why the loss of : 
sensation also is on the side opposite the injury or | 
disease of the brain : for there is no evidence of a 
decussation of posterior fibres like that which ensues 
among the anterior fibres of the medulla oblongata. 
But the discoveries of Brown- Sequard have shown that 
the crossing of sensitive impressions occurs in the spinal 
cord (see p. 498). 

The functions of the medulla oblongata as a nerve-centre 
seem to be more immediately important to the maintenance 
of life than those of any other part of the nervous system, 
since from it alone, or in chief measure, appears to be 
reflected the nervous force necessary for the performance of 
respiration and deglutition. It has been proved by repeated 
experiments on the lower animals that the entire brain 
may be gradually cut away in successive portions, and yet 
life may continue for a considerable time, and the respiratory 



514 THE NEEVOC'S SYSTEM. 

movements be uninterrupted. Life may also continue when 
the spinal cord is cut away in successive portions from 
below upwards as high as the point of origin of the phrenic 
nerve, or in animals without a diaphragm, such as birds or 
reptiles, even as high as the medulla oblongata. In Am- 
phibia, these two experiments have been combined : the 
brain being all removed from above, and the cord from 
below ; and so long as the medulla oblongata was intact, 
respiration and life were maintained. But if, in any animal, 
the medulla oblongata is wounded, 'particularly if it is 
wounded [in its central part, opposite the origin of the 
pneumogastric nerves, the respiratory movements cease, 
and the animal dies as if asphyxiated. And this effect 
ensues even when all parts of the nervous system, except 
the medulla oblongata, are left intact. 

Injury and disease in men prove the same as these ex- 
periments on animals. Numerous instances are recorded 
in which injury to the human medulla oblongata has 
produced instantaneous death ; and, indeed, it is through 
injury of it, or of the part of the cord connecting it with 
the origin of the phrenic nerve, that death is commonly 
produced in fractures and diseases with sudden displace- 
ment of the upper cervical vertebrae. 

The centre whence the nervous force for the production 
of combined respiratory movements appears to issue is in 
the interior of that part of the medulla oblongata from 
which the pneumogastric nerves arise ; for -with care the 
medulla oblongata may be divided to within a few lines of 
this part, and its exterior may be removed without the 
stoppage of respiration ; but it immediately ceases when 
this part is invaded. This is not because the integrity of 
the pneumogastric nerves is essential to the respiratory 
movements ; for both these nerves may be divided without 
more immediate effect than a retardation of these move- 
ments. The conclusion, therefore, may safely be, that 
this part of the medulla oblongata is the nervous centre 



FUNCTIONS OF THE MEDULLA OBLONGATA. 515 

whereby the impulses producing the respiratory move- 
ments are reflected. 

The power by which the medulla oblongata governs and 
combines the action of various muscles for the respiratory 
movements, is an instance of the power of reflexion ^ which 
it possesses in common with all nervous centres. Its 
general mode of action, as well as the degrees to which 
the mind may take part in respiration, and the number 
of nerves and muscles which, under the governance of the 
medulla oblongata, may be combined in the forcible respi- 
Tatory movements, have been already briefly described (see 
p. 225 et seg.). That which seems most peculiar in this 
centre of respiratory action is its wide range of connection, 
the number of nerves by which the centripetal impression 
to excite motion may be conducted, and the number and 
distance of those through which the motor impulse may be 
directed. The principal centripetal nerves engaged in 
respiration are the pneumogastric, whose branches supply- 
ing the lungs appear to convey the most acute impression 
of the ''necessity of breathing." When they are both 
divided, the respiration becomes slower (J. Reid), as if the 
necessity were less acutely felt : but it does not cease, and 
therefore other nerves besides them must have the power 
of conducting the like impression. The experiments of 
Volkmann make it probable that all centripetal nerves 
possess it in some degree, and that the existence of imper- 
fectly aerated blood in contact with any of them acts as a 
stimulus, which, being conveyed to the medulla oblongata, 
is reflected to the nerves of the respiratory muscles : so 
that respiratory movements do not whoUy cease so long as 
any centripetal nerves, and any nerve supplying muscles 
of respiration, are both in continuous connection with the 
respiratory centre of the medulla oblongata. The circulation 
of imperfectly aerated blood in the medulla oblongata itself 
may also act as a stimulus, and react through this nerve- 
centre on the nerves which supply the inspiratory muscles. 

L L 2 



5l6 THE NEEYOUS SYSTEM. 

The wide extent of connection wliicli belongs to tlie 
medulla oblongata as the centre of the respiratorj' move- 
ments, is further shown by the fact that impressions by 
mechanical and other ordinary stimuli, made on many 
parts of the external or internal surface of the body, may 
induce respiratory movements. Thus involuntary respira- 
tions are induced by the sudden contact of cold with any 
part of the skin, as in dashing cold water into the face. 
Irritation of the mucous membrane of the nose produces 
sneezing. Irritation in the pharynx, oesophagus, stomach, 
or intestines, excites the concurrence of the respiratory 
movements to produce vomiting. Violent irritation in the 
rectum, bladder, or uterus, gives rise to a concurrent action 
of the respiratory muscles, so as to effect the expulsion of 
the faeces, urine, or foetus. 

The medulla oblongata appears to be the centre whence 
are derived the motor impulses enabling the muscles of 
the palate, pharynx, and oesophagus, to produce the suc- 
i cessive co-ordinate and adapted movements necessa ry ta 
1 the act of deglutition (see p. 263). This is proved by the 
1 persistence of swallowing in some of the lower animals- 
/ after destruction of the cerebral hemispheres and cerebel- 
lum ; its existence in anencephalous monsters ; the power 
of swallowing possessed by Inarsupial embryoes before the 
CvU-^H/lr]). "brain is developed; and by the complete arrest of the 
power of swallowing when the medulla oblongata is injured 
in experiments. But the reflecting power herein exercised 
by the medulla oblongata is of a much simpler and more 
restricted kind than that exercised in respiration ; it iSy 
indeed, not more than a simple instance of reflex action by 
a segment of the spinal axis, receiving impressions for this 
purpose from only a few centripetal nerves, and reflecting 
them to the motor nerves of the same organ. The incident 
or centripetal nerves in this case are the branches of the 
glossopharyngeal, and, in a subordinate degree, those of 
the fifth nerve, seme of the branches of the su]^^ erior larjn- 



FUNCTIOXS OF THE MEDULLA OBLONGATA. 517 

geal nerve, which are distributed to the pharynx ; and the 
nerves through which the motor impressions to the fauces 
and pharynx are reflected, are the pharyngeal branches of 
ihe vagus, and, in subordinate degrees, or as supplying 
muscles accessory to the movements of the pharynx, the 
branches of the hypoglossal, facial, cervical, recurrent, and 
fifth nerves. For the oesophageal movements, so far as 
ihey are connected with the medulla oblongata, the fila- 
ments of the pneumogastric nerve alone, which contain 
both afferent and efferent fibres, appear to be sufficient 
(John Reid). 

Though respiration and life continue while the medulla; 
oblongata is perfect and in connection with respiratory 
nerves, yet, when all the brain above it is removed, there 
is no more appearance of sensation, or will, or of any 
mental act in the animal, the subject of the experiment, 
than there is when only a spinal cord is left. The move- 
ments are all involuntary and unfelt; and the medulla 
oblongata has, therefore, no claim to be considered as an 
organ of the mind, or as the seat of sensation or volun- 
tary power. These are connected with parts next to be 
■described. 

It would appear that much of the reflecting power of 
the medulla oblongata may be destroyed; and yet its 
power in the respiratory movements may remain. Thus, 
in patients completely affected with chloroform, the wink- 
ing of the eye-lids ceases, and irritation of the pharynx 
-will not produce the usual movements of swallowing, or 
the closure of the glottis (so that blood may run quietly 
into the stomach, or even into the lungs) ; yet, with all 
this, they may breathe steadily, and show that the power 
of tho medulla oblongata to combine in action all the 
nerves of the respiratory muscles is perfect. 

In addition to its influence over the functions of respira- 
tion and deglutition, the medulla oblongata appears to be 
largely concerned also in the faculty of speech. 



5l8 THE NERVOUS SYSTEM. 

la the medulla oblongata appears to be seated also the 
chief vasoj-motor nerve-centre (p. S7^)- From this arise 
fibres which, passing down the spinal cord, issue with the 
anterior roots of the spinal nerves, and enter the ganglia 
and branches of the sympathetic, by which they are 
conducted to the blood-vessels. 

The influence which is exercised by the medulla ob- 
longata, or, at least, by its irritation, on the formation of 
sugar in the liver, has been referred to (p. 336). 



STBUCTURE AND PHYSIOLOGY OF THE POKS TAEOLTI, 
CRimA CEREBKI, CORPOKA QUADRIGEMINA, CORPORA 
GENICULATA, OPTIC THALAMI, AND CORPORA STRIATA. 

Fons Varolii. — The meso-cephalon, or pons (ti, fig. 145) 
is composed principally of transverse fibres connecting the 
two hemispheres of the cerebellum, and forming its prin- 
cipal commissure. But it includes, interlacing with these, 
numerous longitudinal fibres which connect the medulla 
oblongata with the cerebrum, and transverse fibres which 
connect it with the cerebellum. Among the fasciculi of 
nerve 'fibres by which these several parts are connected, 
the pons also contains abundant grey or vesicular sub- 
stance, which appears irregularly placed among the fibres, 
and fills up all the interstices. 

The anatomical distribution of the fibres, both trans- 
verse and longitudinal, of which the pons is composed, is 
sufficient evidence of its functions as a conductor of im- 
pressions from one part of the cerebro- spinal axis to 
another. 

Concerning its functions as a nerve-centre, little or 
nothing is certainly known. 

Crura Cerebri. — The crura cerebri (iii, fig. 145), are prin- 
cipally formed of nerve-fibres, of which the inferior or more 
superficial are continuous with those of the anterior pyra- 



THE PONS VAEOLII. 



519 



inidal tracts of the medulla oblongata, and the superior or 
deeper fibres Tvith the lateral and posterior pyramidal tracts, 
and with the olivary fasciculus. Besides these fibres from 
the medulla oblongata, are others from the cerebellum and 

Fig. 145 /•= 




some of the latter as well as a part of the fibres derived 
from the lateral tract of the medulla oblongata, decussate 
across the middle line. 



* Fig. 145. Base of the brain (from Quain). J. — i, superior longi- 
tudinal fissure ; 2, 2', 2", anterior cerebral lobe ; 3, fissure of Sylvius, 
between anterior and 4, 4', 4", middle cerebral lobe ; 5, 5', posterior 
lobe ; 6, medulla oblongata ; the figure is in the right anterior pyra- 
mid ; 7, 8, 9, 10, the cerebellum ; + , the inferior vermiform jirocess. 
The figures from I. to IX. are placed against the corresponding 
cerebral nerves ; III. is placed on the right crus cerebri ; YL and VII. 
on the pons Yarolii ; X. the first cervical or suboccipital nerve. 



520 THE NERVOUS SYSTEM. 

On their upper part the crura cerebri bear three pairs 
of small ganglia, or masses of mingled grey and white 
nerve-substance, namely, the corpora geniculata externa 
and interna, and the corjyora quadrigemina, or nates amditestes. 
And in their onward course to the cerebrum, the fibres of 
each cms cerebri pass through two large ganglia, the optic 
thalamus and corpus striatum, and in their substance come 
into connection with variously-shaped masses and layers 
of grey substance. Whether all the fibres of the crura 
cerebri end in the grey matter of these two ganglia, while 
others start afresh from them to enter the cerebral hemi- 
spheres ; or whether some of the fibres of the crura pass 
through them, while only a portion can be strictly said to 
have their termination there, must remain at present 
undecided; the difiiculties in the way of solving such an 
anatomical doubt being at present insuperable. 

Each crus cerebri contains among its fibres a mass of 
vesicular substance, the locus niger, the nerve-corpuscles of 
which abound in pigment-granules, and afi'ord some of the 
best instances of the caudate structure. 

With regard to their functions, the crura cerebri may 
be regarded as, principally, conducting organs. As nerve- 
centres they are probably connected with the functions of 
the third cerebral nerve, which arises from the locus niger, 
and through which are directed the chief of the numerous 
and complicated movements of the eyeball and iris. 

From the result of vivisection it appears that when one 
of the crura cerebri is cut across, the animal moves round 
and round, rotating around a vertical axis from the injured 
towards the sound side. Such movements, however, attend 
the sections of other parts than the crura cerebri : 
and as indications of the functions of these parts, the 
results of such experiments have been hitherto almost 
valueless. 

Corpora Quadrigemina. — ^The corpora quadrigemina (from 



FUNCTIOJ^S OF THE SENSORY GANGLIA. 52 1 

which, in function, the corjjora geniculata are not distin- / 
guished), are the homologues of the optic lobes in birds, . 
Amphibia and fishes, and may be regarded as the prin- -. 
cipal nervous centres for the sense of si^ht. The experi- \ 
ments of~Flourens, Longet, and Hertwig, show that 
removal of the corpora quadrigemina wholly destroys the 
power of seeing ; and diseases in which they are disor- 
ganized are usually accompanied with blindness. Atrophy 
of them is also often a consequence of atrophy of the eyes. 

Destruction of one of the corpora quadrigemina (or of 
one optic lobe in birds), produces blindness of the oppo- \ 
site eye. 

This loss of sight is the only apparent injury of 
sensibility sustained by the removal of the corpora quad- 
rigemina. The removal of one of them affects the move- 
ments of the body, so that animals rotate, as after division 
of the cms cerebri, only more slowly : but this is probably 
due to giddiness and partial loss of sight. The more 
evident and direct influence is that produced on the iris. 
It contracts when the corpora quadrigemina are irritated : 
it is always dilaied when they are removed : so that they 
may be regarded, in some measure at least, as the nervous 
centres governing its movements, and adapting them tO' 
the impressions derived from the retina through the optic 
nerves and tracts. 

Concerning the functions, taken as a whole, discharged by 
the olfactory and optic lobes, the grey substance of the pons, 
the corpora striata and optic thalami (6, d, fig. 146), with 
some other centres of grey matter not so distinct, such as the 
grey matter on the floor of the fourth ventricle with which 
the auditory nerve is connected, the most philosophical 
theory is undoubtedly that which has been so ably enun- 
ciated by Dr. Carpenter. He supposes these ganglia to 
constitute the real sensorium ; that is to say, it is by means 
of them that the mind becomes conscious of impressions 



522 THE NERVOUS SYSTEM. 

made on the organs or tissues witli \rhicli (by means of 
Fig. 146.* 



* Fig. 146. Dissection of brain, from above, exposing the lateral, 
fourth, and fifth ventiicles, with the surrounding parts (from Hirsch- 
feld and Leveille). h — a, anterior part, or gcniu of corpus callosum ; 
Z>, corpus striatum ; h', the corpus striatum of left side, dissected so as 
to expose its grey substance ; c, points by a line to the taenia semicu- 
laris ; d, optic thalamus ; e, anterior pillars of fornix divided ; below 
they are seen descending in front of the third ventricle, and between 
them is seen part of the anterior commissure ; in front of the letter e 
is seen the slit-lilce fifth ventricle, between the two laminse of the 
septum lucidum ; /, soft or middle commissure ; g is placed in the pos- 
terior part of the third ventricle ; immediately behind the latter are 
the posterior commissure (just visible) and the pineal gland, the two 
crura of which extend forwards along the inner and upper margins of 
the optic thalami ; h and i, the corpora quadrigemina ; k, superior 
<;rus of cerebellum ; close to k is the valve of Vieussens, which has 
been divided so as to e xpose the fourth ventricle ; /, hippocampus 



THE CEKEBELLU^^r. 



523 



nerve -fibres) they are in communication. Tlius impres- 
sions made on the optic nerve, or its expansion in the 
retina, are conducted by the fibres of the optic nerve to 
the 'corpora quadrigemina, and through the medium of 
these ganglia the mind becomes conscious of the impres- 
sion made. And impressions on the filaments of the 
olfactory or auditory nerve are in the same way perceived 
through the medium of the olfactory or auditory ganglia, 
to which they are first conveyed. The optic thalami and 
corpora striata probably have some function of a like kind 
— perhaps in relation to ordinary sensation, but nothing is 
certainly known regarding them. 

Besides their functions, however, as media of communi- 
cation between the mind and external objects, these sensory 
ganglia, as they are termed, are probably the nerve-centres 
by means of which those reflex acts are performed which 
require either a higher combination of muscular acts than 
can be directed by means of the medulla oblongata or 
spinal cord alone, or on the other hand, such reflex actions 
as require for their right performance the g-uidance of 
sensation. U'lder this head are included various acts, as 
walking, reading, writing, and the like, which we are 
accustomed to consider voluntary, but which really are as 
incapable of being performed by distinct and definite acts 
of the will as are those more simple movements of which 
we are not conscious, and which, performed under the 
guidance of the spinal cord or medulla oblongata alone, 
we call simple reflex actions. It is true that in the per- 
formance of such acts as those just-mentioned, a certain 
exercise of the will is required at the commencement, but 
that the carrying out of its mandates is essentially reflex 

major and corpus finibriatum, or taenia hippocampi ; m, hippocampus 
minor ; n, eminentia collateralis ; 0, fourth ventricle ; ^>, posterior 
surface of medulla oblongata ; r, section of cerebeilmn ; s, upper part 
of left hemisphere of cerebellum exposed by the removal of part of the 
posterior cerebral lobe. 



524 ^ THE XERVOUS SYSTE:M. 

and involuntary, anyone may convince himself by trying 
to perform each individual movement concerned, strictly 
as a voluntary act. 

That such movements are reflex and essentially inde- 
pendent — as regards their mere production — of the will, 
there is no doubt : that the nerve-centres through which 
such reflex actions are performed are the so-called sensory 
ganglia, is, of course, only a theory which may or not be 
confirmed by future investigations. 

Besides their possible functions in the manner just men- 
tioned, it is supposed that these sensory ganglia may be 
the means of transmitting the impulses of the will to the 
muscles, which act in obedience to it, and thus be the 
centres of reflex action as well for impressions conveyed 
downwards to them from the cerebral hemispheres, as for 
impressions carried upwards to them by the different nerves 
which preserve their connection with the organs of the 
various senses. 



STKTJCTUKE AXD PHYSIOLOGY OF THE CEREBELLUM. 

The cerebellum (7, 8, 9, 10, fig. 147) is composed of an 
elongated central portion called the vermiform processes, 
and two hemispheres. Each hemisphere is connected with 
its fellow, not only by means of the vermiform processes, 
but also by a bundle of fibres called the middle cms or 
peduncle (the latter forming the greater part of the pons 
Varolii), while a superior cms with the valve of Vieussens, 
connects it with the cerebrum (fig. 147, 5,) and an inferior 
<-ms (formed by the prolonged restiform body) connects it 
with the medulla oblongata (3, fig. 147). 

The cerebellum is composed of white and grey matter 
like that of the cerebrum, but arranged after a diff'erent 
fashion as shown in fig. 147. 

Besides the grey substances on the surface, however, 
there is near the centre of the white substance of each 



rUNCTIOXS OF THE CEKEBELLUM. 



525 



hemispliere, a small capsule of grey matter called the 
corpus dentatum (fig. 148, erf), resembling very closely tlie 

Fig. I47-* 




corpus dentatum of the olivary body of the medulla oblon- 
gata (fig. 148, j). 

The physiology of the cerebellum may be considered in 
its relation to sensation, voluntary motion, and the instincts 
or higher faculties of the mind. It is itself insensible to 
irritation, and may be all cut away without eliciting signs 



* Fig. 147. View of cerebellum in section and of fourth ventricle, 
with the neighbouring parts (from Sappey after Hirsclifeld and Le- 
veilld). I, median gi'oove of fourth ventricle, ending below in the 
calamus scrix>torms, Avith the longitudinal eminences formed by the 
fasciculi teretes one on each side ; 2, the same gi-oove, at the place 
where the white streaks of the auditory nerve emerge from it to cross 
the floor of the ventricle ; 3, inferior crus or penduncle of the cere- 
bellum, formed by the restiforni body ; 4, posterior pyrami<l ; above 
this is the calamus scriptorius ; 5, superior crus of cerebellum, or pro- 
cessus a cerebello ad cerebrum (or ad testes) ; 6, 6, fillet to the side of 
the crura cerebri ; 7, 7, lateral grooves of the crura cerebri ; "8, corpora 
quadrigemina. 



526 THE NERVOUS STSTEil. 

of pain (Longet). Yet, if any of its crura be touched, pain 
is indicated ; and, if tlie restiforni tracts of the medulla 
oblongata be irritated, the most acute suffering appears to 
be produced. Its removal or disorganization by disease is 
also generally unaccompanied with loss or disorder of 
sensibility ; animals from which, it is removed can smell, 
see, hear, and feel pain, to all appearance, as perfectly as 

Firj. 148* 




before (Flourens; Magendie). So that, although the resti- 
form tracts of the medulla oblongata, which themselves 
appear so sensitive, enter the cerebellum, it cannot be re- 
garded as a principal organ of sensibility. 

In reference to motion, the experiments of Longet and 
most others agree that no irritation of the cerebellum 
produces movement of any kind. Remarkable results, 



* Fig. 148. Outline sketch of a section of the cerebellum, showing 
tlie corpus dentatum (from Quain). f. — The section has been earned 
thi-ough the left lateral part of the pons, so as to divide the superior 
peduncle and pass nearly through the middle of the left cerebellar hemi- 
sphere. The olivary body has also been divided longitudinally so as to 
expose in section its corpus dentatum. c r, cms cerebri ; /, fillet ; q, 
corpora ([uadrigemina ; s^j, supeiior peduncle of the cerebellum divided ; 
on p, middle peduncle or lateral part of the pons Varolii, Avith fibres 
passing from it into the ■white stem ; a v, continuation of the white stem 
radiating towards the arbor vita? of the folia ; c cZ, coi*pus dentatum ; 0, 
olivary body with its corpus dentatum ; p, anterior pyramid. 



FUNCTIOXS OF THE CEEEBELLUM. 527 

however, are produced by removing parts of its substance. 
Flourens (whose experiments have been abundantly con- 
firmed by those of Bouillaud, Longet, and others) extir- 
ipated the cerebellum in birds by successive layers. Feeble- 
ness and want of harmony of the movements were the 
consequence of removing the superficial layers. When he 
reached the middle layers, the animals became restless 
without being convulsed ; their movements were violent 
and irregular, but their sight and hearing were perfect. 
By the time that the last portion of the organ was cut 
away, the animals had entirely lost the powers of spring- 
ing, flying, walking, standing, and preserving their equi- 
librium. When an animal in this state was laid upon its. 
back, it could not recover its former posture ; but it 
fluttered its wings and did not lie in a state of stupor ; it 
saw the blow that threatened it, and endeavoured to avoid 
it. Volition, sensation, and memory, therefore, were not 
lost, but merely the faculty of combining the actions of the 
m^uscles ; and the endeavours of the animal to maintain its 
balance were like those of a drunken man. 

The experiments afibrded the same results when repeated 
on all classes of animals ; and, from them and the others 
before referred to, Flourens inferred that the cerebellum 
belongs neither to the sensitive nor the intellectual appa- 
ratus ; and that it is not the source of voluntary movements, 
although it belongs to the motor-apparatus ; but is the 
organ for the co-ordination of the voluntary movements, or 
for the excitement of the combined action of muscles. 

Such evidence as can be obtained from cases of disease of 
this organ confirms the view taken by Flourens ; and, on 
the whole, it gains support from comparative anatomy; 
animals whose natural movements require most frequent 
and exact combinations of muscular actions being those 
whose cerebella are most developed in proportion to the 
spinal cord. 

M. Fovilie holds that the cerebellum is the organ of 



528 THE XEEYOUS SYSTEM. 

muscular sense, i.e., the organ by wHch. the mind acquires 
that knowledge of the actual state and position of the 
muscles which is essential to the exercise of the will upon 
them ; and it must be admitted that all the facts just 
referred to are as well explained on this hypothesis as on 
that of the cerebellum being the organ for combining 
movements. A harmonious combination of muscular 
actions must depend as much on the capability of appre- 
ciating the condition of the muscles with regard to their 
tension, and to the force with which they are contracting, 
as on the power which any special nerve-centre may possess 
of exciting them to contraction. And it is because the 
power of such harmonious movement would be equally 
lost, whether the injury to the cerebellum involved injury 
to the seat of muscular sense, or to the centre for com- 
bining muscular actions, that experiments on the subject 
afford no proof in one direction more than the other. 

Gall was led to believe, that the cerebellum is the organ 
of physical love, or, as Spurzheim called it, of amativeness; 
and this view is generally received by phrenologists. The 
facts favouring it are, first, several cases in which atrophy 
of the testes and loss of sexual passion have been the 
consequence of blows over the cerebellum, or wounds of its 
substance ; secondly, cases in which disease of the cere- 
bellum has been attended with almost constant erection of 
the penis, and frequent seminal emissions ; and thirdly, 
that it has seemed possible to estimate the degree of sexual 
passion in different persons by an external examination of 
the region of the cerebellum. 

The cases of disease of the cerebellum do not prove 
much ; for the same affections of the genital organs are 
more generally observed in diseases, and in experimental 
irritations of the medulla oblongata and upper part of the 
spinal cord (Longet). 

The facts drawn from craniological examination will 
receive the credit given to the system of which they are a 



FUNCTIONS OF THE CEREBELLUM. 529 

principal evidence. But, in opposition to them, it must be 
stated that there has been a case of complete disorganiza- 
tion or absence of the cerebellum without loss of sexual 
passion (Combiette, Longet, and Cruveilhier) ; that the 
cocks from whom M. Flourens removed the cerebellum 
showed sexual desire, though they were incapable of 
gratifying it ; and that among animals there is no pro- 
portion observable between the size of the cerebellum and 
the development of the sexual passion. On the con- 
trary, many instances may be mentioned in which a larger 
sexual appetite co-exists with: a smaller cerebellum; as 
e.g.f that rays and eels, which are among the fish that 
copulate, have not laminae on their almost rudimental 
cerebella; and that cod-fish, which do not copulate, but 
deposit their generative fluids in the water, have com- 
paratively well- developed cerebella. Among the Amphibia, 
the sexual passion is apparently very strong in frogs and 
toads ; yet the cerebellum is only a narrow bar of nervous 
substance. Among birds there is no enlargement of the 
cerebellum in the males that are polygamous ; the domestic 
cock's cerebellum is not larger than the hen's, though his 
sexual passion must be estimated at many times greater 
than hers. Among Mammalia the same rule holds ; and 
in this class the experiments of M. Lassaigne have plainly 
shown that the abolition of the sexual passion by removal 
of the testes in early life is not followed by any diminu- 
tion of the cerebellum ; for in mares and stallions the 
average absolute weight of the cerebellum is 6 1 grains, 
and in geldings 70 grains ; and its proportionate weight, 
compared with that of the cerebrum, is, on average, as 
I : 6-59 in mares; as I : 5-97 in geldings, and only as 
I : 7*07 in stallions. 

On the whole, therefore, it appears advisable to wait for 
more evidence before concluding that there is any peculiar 
and direct connection between the cerebellum and the 
sexual instinct or sexual passion. From aU that ha& 



530 THE NERVOUS SYSTEM. 

been observed, no other office is manifest in it than tbat 
of regulating and combining muscular movements, or of 
enabling them to be regulated and combined by so inform- 
ing the mind of the state and position of the muscles that 
the will may be definitely and aptly directed to them. 

The influence of each half of the cerebellum is directed 
to muscles on the opposite side of the body ; and it would 
appear that for the right ordering of movements, the 
actions of its two halves must be always mutually balanced 
and adjusted. For if one of its crura, or if the pons on 
either side of the middle line, be divided, so as to cut off 
from the medulla oblongata and spinal cord the influence 
of one of the hemispheres of the cerebellum, strangely 
disordered movements ensue. The animals fall down on 
the side opposite to that on which the crus cerebelli has 
been divided, and then roll over continuously and re- 
peatedly ; the rotation being always round the long axis 
of their bodies, and from the side on which the injury has 
been inflicted.^' The rotations sometimes take place with 
much rapidity; as often, according to M. Magendie, as 
sixty times in a minute, and may last for several days. 
Similar movements have been observed in men ; as by M. 
Serres in a man in whom there was apoplectic effusion in 
the right crus cerebelli; and by M. Belhomme in a woman, 
in whom an exostosis pressed on the left crus.f They 



* Magendie and Miiller, and others following him, say the rotation 
is towards the injured side ; but Longet and others more correctly give 
the statement as in the text. The difference has probably arisen from 
using the words right and left, without sajang whose right and left are 
meant, whether those of the observer or those of the observed. "When, 
for example, an animal's right crus cerebelli is divided, he rolls from his 
own right to his own left, but fi-om the left to the right of one who is 
standing in front of him. 

t See such cases collected and recorded by Dr. Paget in the Ed. Med. 
and Surg. Journal for 1847. 



FUNCTIONS OF THE CEREBRUM. 531 

may, perhaps, be explained by assuming that the division 
or injury of the crus cerebelli produces paralysis or 
imperfect and disorderly movements of the opposite side 
of the body ; the animal falls, and then, struggling with 
the disordered side on the ground, and striving to rise with 
the other, pushes itself over; and so, again and again, 
with the same act, rotates itself. Such movements cease 
when the other crus cerebelli is divided ; but probably only 
because the paralysis of the body is thus made almost 
complete. 

'sTKTJCTirEE AND PHYSIOLOGY OF THE CEREBRUM. 

The cerebrum is placed in connection with the pons and 
medulla oblongata by its two "cmr^ or peduncles (fig. 149) : 
it is connected with the cerebellum, by the processes called 
superior crura of the cerebellum, or processus a cerehello ad 
testes, and by a layer of grey matter, called the valve of 
Vieussens, which lies between these processes, and extends 
from the inferior vermiform process of the cerebellum to 
the corpora quadrigemina of the cerebrum. These parts, 
which thus connect the cerebrum with the other princi- 
pal divisions of the cerebro-spinal nervous centre, form 
parts of the walls of a cavity (the fourth ventricle) and a 
canal (the iter a tertio ad guartum ventriculum) which are 
the continuation of the canal that in the foetus extended 
through the whole length of the spinal cord and brain. 
They may, therefore, be regarded as the continuation of 
the cerebro-spinal axis or column ; on which, as a develop- 
ment from the simple type, the cerebellum is placed ; and, 
on the further continuation of which, structures both larger 
and more numerous are raised, to form the cerebrum 
(fig. 142). 

The cerebral convolutions appear to be formed of nearly 
parallel plates of fibres, the ends of which are turned 
towards the surface of the brain, and are overlaid and 

M M 2 



532 THE NERVOUS SYSTEM. 

mingled with successive layers of grey nerve- substance. 
The external grey matter is so arranged in layers, that a 
vertical section of a convolution, according to Mr. Lockhart 




Clarke, generally presents the appearance ot seven layers 
of pale and dark nervous substance. The structure of the 
grey matter is that which belongs to vesicular nervous 
substance (p. 473). 

It is nearly certain that the cerebral hemispheres are 
the organs by which, — ist, we perceive those clear and 
more impressive sensations which we can retain, and 



* Fig. 149. Plan